Engine Tuning, Remaps, Fuel Saving

What is Remapping?

Most modern vehicles contain an ECU (or Engine Control Unit) that is a small computer which controls how the engine performs. it decides based on information from sensors and the drivers inputs how, much fuel and the timing of ignition or injection or both.
Vehicle manufacturers de-tune the engine by setting the software on the ECU to safe levels.
This is done due to the manufacturers having to sell their cars all over the world, this means that the software settings on the ECU must take into account different climates, laws & restrictions and varying quality of fuels. Not to mention irregular servicing and poor quality lubricants and filters.
Vehicle remapping is basically the modification/replacement of the manufactures default software on a vehicles ECU, to optimise the settings for our temperate climate, good quality fuel supply and regular servicing.

How is it done?

A vehicle remap replaces default software on the ECU, overwriting it with new software which can be programmed to optimize the cars overall performance. This is known as vehicle remapping because the ECU is essentially a program that controls how the engine is controlled. When your car is remapped, the tuned software is plugged into your cars serial port (or OBD port) which then overwrites the engine map with the new version to enhance engine performance. The ability to flash directly through the OBD has brought the tuning industry on leaps and bounds, with constant development on the engine now being much quicker via the flash process.
It has its drawbacks however as now anyone can remap your car, not just the specialist tuning companies.
Every couple of years the vehicle manufacturers improve the security of their software, which prevents remapping via the OBD port.
This is what is happening right now.
For newer vehicles the ECU has to be removed then opened and boot pins connected to the ECU circuit board. This is not for the faint hearted, and requires specialist up to date equipment.

It cannot be done with cheap clone tooling.
This will once again remove the cowboys from the industry, for a while at least.

Maths Test ( Ford Transit P0121) Pedal Position sensor circuit performance

Maths Test

A Ford  Transit was presented with a fault code stored for accelerator pedal performance.
DTC P0121- Throttle/Pedal Position Sensor/Switch 'A' Circuit Range/Performance.

Information systems suggest the causes for such a fault are;
- Faulty throttle position sensor
- Throttle position sensor harness is open or shorted
- Throttle position sensor circuit poor electrical connection
- Faulty Engine Control Module (ECM)


The easy option is to replace the pedal, but we prefer to test the component plus the power, ground and signal wires before condemning any parts or control modules.
It may take longer than picking up the phone and ordering the suspected part but it is a vital step in the diagnostic process.

The easiest way of testing the complete circuit is to use an oscilloscope.

Most older pedal position sensors use a variable resistance track that changes the voltage sent back to the module which is converted into a pedal position.
This method uses an analogue signal, which must be converted inside the module into a digital signal.

Some newer vehicles employ a digital sensor which can be utilised by the module without any further processing of the signal.
The sensor output is a fixed frequency variable duty signal which can be tricky to interrupt using the oscilloscope.
Check out the scope trace of the pedal signal.

This one test shows that the power and ground is good as well as proving the change in pulse width. 

The problem is checking the smooth transition from the idle position to Wide open throttle.

The use of a built in maths channel to display duty cycle is very useful.

To display the Duty Cycle on a Pico Scope you need to select Tools> maths channels>Create>Advanced>Duty>A>Next>Next>Next>Finish>Ok>

You should then end up with a trace like this;

It is now much easier to analyse the performance of the pedal sensor. Note the smooth transition from idle to WOT.

Diverter Valve VAG

We are still seeing plenty of diverter valve (DV) failures here at Gotboost.

The original factory diaphragm can crack under high boost pressure and create a massive boost leak. The new OEM valve features an upgraded piston type design modeled after the more expensive aftermarket units. This is the perfect solution for anybody needing an upgraded DV that does not want to void their factory warranty with "aftermarket" parts
The DV is a pathway for boost when it is not being used by your engine. Whenever the throttle body is closed, such as during gear shifts or deceleration, the boost needs an escape route or the pressure will build up and slow down the compressor. This can cause turbo lag or even damage the turbo.
A Blow Off Valve (BOV) or dump valve performs the same task as a Diverter Valve, but instead of returning the boosted air back into the intake, it vents it to the atmosphere making a distinctive noise.
We can replace your DV with the uprated part for just £76.25.

Boost got you under pressure

A Honda Civic Type R with a Jackson racing supercharger conversion was presented with major running problems.

It runs with a Hondata ECU which has proved itself to be very reliable and more than capable of running this conversion many times.
So why was this one idling at 2500 rpm and almost un-drivable?

With such a popular conversion, it was easy to find information.
This provided us with base maps, tuning specifications and hardware requirements.

The first thing to do was check for fault codes, however there were no codes stored.
So we connected the basic logging equipment to the vehicle and attempted to drive it on the dyno.
The result was extremely poor fuelling and massive overboost.

We now had a problem. The hardware was not compatible with the vehicle.
A change of supercharger pulley diameter was required.
Once this was completed the boost pressure was now within acceptable limits. But the car was still not right.

Looking at the map stored on the ECU, during testing it appeared to have some very poor calibrations.
The answer was a base map from a similar specification car. This is then fine tuned to suit the vehicle. In this case reducing the knock counter at certain load and rpm ranges by trimming the advance curve.

The result was night and day. The car now pulled like a train and recorded a very healthy 188BHP at the wheels or around 240BHP at the flywheel.

Why is it so hard to sell the concept of training to the UK automotive aftermarket?

Given the complexity of the modern vehicle, you would expect technicians to require regular updates about the advances in vehicle technology.
So why is it so difficult to persuade garages to train staff?
Why do technicians not want to advance their learning?

Most garages are aware of the skills gap they face, but they opt for the ostrich approach and ignore the problem. A common mistake is buying diagnostic tools and not taking advantage of the training that is provided. Instead the technician muddles on, doing what he always did. Getting what he always got.

I had a set of tyres fitted recently and I watched the tyre fitter closely.
He didn't remove the wheel weights before balancing the wheel, this resulted in a large number of weights being fitted without achieving dynamic balance.
He used an air gun to tighten the wheel nuts, then checked the torque using a wrench which clicked immediately meaning the wheel nuts were already over tightened.

When paying the bill, I asked the manager (his badge said he was anyhow) about the short comings in the procedures used by his staff. His reply was they needed training.

Great news, so I left my card, and waited for the call. After a week or so I called the garage. Offered my services and reminded the manager that a few hours training would make the garage more efficient, profitable and improve customer satisfaction. He response was he had no time for training.

I wonder how they are getting along with run flats, tyre pressure monitoring, and 4 wheel alignment seeing as they couldn't balance a tyre and tighten the wheel nuts correctly.

Vectra Light failure

Modern cars have the ability to monitor circuits and report errors when they are detected.

Modern light systems have the ability to warn the driver that a circuit failure has occurred with a Malfunction Indicator Lamp. The driver can then take the car to the workshop for diagnosis and repair.

The owner of one such vehicle was certain that he faced an expensive repair when the lighting circuit MIL illuminated on his Vauxhall, but when he checked the lights he could not find the one not working.

A quick code read suggested a fault with the rear left brake light circuit. However the brake lamps appeared to be working when the pedal was pressed. The light cluster was accessed and the lamps checked. The nearside brake lamp had indeed failed.

This led to a number of questions from the puzzled driver.

So how did the car know?

Why are all the lamps the same?

Why did the lamp appear to work when the pedal was pressed?

The answers are linked to how modern lighting circuits are controlled. The use of vehicle networks has reduced the number of fuses and relays by as much as half. But every circuit must have a form of protection, in the case of modern lighting it is the control unit that monitors the current drawn by circuits. It can then switch the circuit off if it detects a fault. It can then elect to use another lamp and circuit to replace the faulty one. In this case the brake light circuit was inoperative so the side light circuit was used to perform the task of the brake light. This is possible as the lights are controlled using a pulse width modulated signal. The brake lights require full intensity so have a pulse width of 100% but the side lights only require around 25% of the 21Watts available. By switching the circuit 278 times a second the 25% duty cycle is seen by the lamp as a 3Volt supply. (This is what you would read on a multi-meter) The 21 Watt lamp illuminates at around a quarter of its intensity, or 5 Watts the same as a tail light. The means the same lamp can perform the task of tail and brake lights. Using just one lamp makes economic sense as it reduces inventory.

The control unit sends a signal to the lamps and checks the circuit before it is used. Here the brake light circuit is being monitored every 10 seconds. The voltage is pulsed so fast that the filament does not even start to glow. This is how the control unit can detect a fault before the circuit is used.

Using an oscilloscope you can check the current draw during the circuit check. Here the time base has been reduced to 1ms per division. The red trace shown indicates a current of 9 Amps on a brake light circuit. This has to be a fault. Or is it?

Once the lamp is switched on (100% duty cycle) the current measured is around 1.7 Amps. This is normal for a 21 Watt lamp.

Watts law current = power/voltage

21/12 = 1.75 Amps.



Same lamp same circuit. Different current draw, this is because once the lamp heats up and starts to glow its resistance increases. Try it for yourself with a multi-meter, measure the resistance of a cold 21 Watt lamp. Then use Ohms law to check to expected current flow.

Remember Amps = Voltage/resistance.

Lost your spark

Modern ignition systems have evolved from contact breaker or points systems. If you look carefully you can still see some of the DNA of these systems in the latest systems fitted today. So is it reasonable to assume that some of the tests performed on older ignition systems can still be performed on these modern systems?

The answer is yes and no. Some of the old tests can still be performed when there is suitable access but many of the tests focused on the High Tension or secondary side of the coil. However access to the high tension side is often only possible after removing the coil pack, you can use an extension between the coil and the plug to test the HT outputs. These tests can be performed with an oscilloscope or a spark tester.

Some (older) readers will remember measuring dwell angles. Testing the LT or primary circuit, has changed little since the days of points, a test lamp can still provide quick and effective proof of circuit integrity. However an oscilloscope can provide extra details that can lead to more effective diagnosis. With an oscilloscope it is possible to analyse the current draw as well as the control signal/voltage at the same time. The reason why this is so important becomes clear when you consider how the modern ignition system is controlled.

Modern ignition systems consist of various inputs, logic and outputs. Inputs are from sensors such as crankshaft position, (engine speed & position) Manifold absolute pressure, or Air Mass (load) and knock sensors (abnormal combustion).

The logic or ECU, crunches the numbers and selects the correct ignition advance, dwell period as well as monitoring the circuit for faults and providing the circuit protection.

The outputs are the low tension circuits, fault codes and malfunction indicator lamp. Or in the case of amplified coils a signal to switch the amplifier and often a conformation of ignition signal back to the ECU.

These control signals can be an internal function of the ECU or in the case of amplified coils a square waveform that is used to switch the primary coil. The on time of the coil is controlled by this signal. The output stage allows current to flow through the primary windings when the voltage is present and stops the flow of current when the voltage drops to 0V. This ‘dwell’ can be measured much like on the older systems. The yellow trace is the control signal and the blue trace is the current flow through the primary windings. 

The cursors are measuring the on time or dwell, in this case 3.16ms. A typical value for a running engine. Notice the coil has reached around 5.5 Amps. Then current in the circuit is limited. The primary coil windings have low resistances, between 0.2 and 0.8 Ohms. This allows a rapid build-up of current, and can reach 60 Amps if left unchecked in around 40ms. The current in the circuit is dependent upon the voltage so to ensure good saturation the ECU can compensate for low voltages. The chart shows the current build up in a coil of 0.2Ω for both 12 and 8 Volts. 

Current Flow Diagram Diagnosis

The ever increasing electrical and electronic content of modern vehicles can make diagnosis and repairs a real challenge.
We have seen a number of faults that without the correct approach, could lead technicians to at best take much longer to diagnose or at worse fail to or misdiagnose.
During training we encourage technicians to analyse how effective their diagnostic routine actually is.
Some have a set routine, others fly by the seat of their pants.
What ever technique you use, could you improve your diagnostic skills?
We have discovered that simple faults can fox even experienced technicians.
Take a simple central locking fault, the vehicle will lock and unlock all doors from the passenger door lock and the remote, but if the drivers door lock is used only the unlock function works.
This suggests to me,a fault with the door lock switch.
But how can this be proved quickly without stripping unnecessary trim from the vehicle.
The wiring or current flow diagram will often hold the key.
We recommend drawing your own diagram, it should contain only the detail you require to test the circuit.
This includes wires colours, pin numbers and what you expect to see on the voltmeter.

Take a look at the diagram below, where is the likely fault, where can you test easily, and what would you expect to see.

When the whole diagram is presented it can be difficult to see the wood from the trees.
However it can be easier with your own diagram. Like the one below.

Testing at the module means the door trim does not have to be removed, if the voltmeter reads 0.1Volts at pins 12, 13 & 9 when the switches make a path to ground then the circuits and switches are OK.
At pin 12 the voltmeter reads 0.1Volt when the passenger door switch is made. But remains at 12Volts when the drivers switch is made. The fault can only be between the switch and the join in the wiring.
As this join is inside the car it is possible to trace the wire, it was found to be broken in the door hinge area, a common failure due to the constant opening and closing of the door. A quick repair and normal operation was restored. All without ordering parts or stripping door trims.

Calm under Pressure

The Peugeot 307 2.0 HDi came into the workshop with a history of failed repairs and an inventry of second hand parts fitted in an attempt to get it running correctly.

We have identified the ECU as the culprit, the internal earth path for the rail pressure sensor has failed.
With the ECU repaired, we could consider what has caused the rail pressure to increase without any command from the ECU.
The engine would start and idle but it would cut out when the rail pressure exceed set limits. (400+ bar)
We monitored the current drawn by the pressure regulator during the pressure increase and it did not alter.
This means the increase in pressure is down to a mechanical fault, not an electrical fault.
All high pressure fault diagnosis must start with the low pressure system.
In this case a higher low pressure could possibly result in higher, high pressure values.
A gauge was set up to monitor the low pressure, and an oscilloscope analysed the high pressure voltage from the rail pressure sensor. (Remember the original fault affected this sensor)
The engine was started and the rail pressure settled to a even 1.3V with a low pressure supply of 4.5 Bar.
Then the engine cut out. The Supply pressure remained constant however the rail pressure increased at the time the engine cut out.

The return lines were checked for damage and they all appeared to be fine, so what is causing the rise in rail pressure?
This is where system understanding is key to the diagnosis. The pressure is regulated by a valve, this valve allows fuel to bleed past to reduce the pressure. It has a spring inside that holds around 80-100 Bar in the rail when there is no current flowing to increase this pressure by means of an electro-magnet forcing the valve closed. A cranking check using live data showed the pressure was in excess of 120Bar in live data with the valve disconnected.

The valve must be sticking or blocked. The valve can be removed for replacement or inspection.
In this case a large amount of metal swarf was found inside the fine filter that is fitted, this must be preventing the fuel escaping. We cleaned the filter and replaced the valve. The swarf must be coming from the fuel system, and without a comprehensive repair history, we could not be certain the fault had been repaired or was the component still breaking down.

Due to the high costs involved it was decided that the best way forward was to return the vehicle to the customer. The vehicle has been driven for 3-5 thousand miles without issue.

HDI rail pressure fault codes

A 2002 Peugeot 307 2.0 HDi was presented with multiple fault codes.

It was in reduced performance mode, and driving the owner and a few local garages crazy.
The codes would clear and return, and the car would drive far better with the air mass meter disconnected.
This has led to incorrect diagnosis of the AMM, and the replacement of many components with 2nd hand parts to try and eliminate the cause all without success.

A quick scan produced the same result as the previous garages, DTC's.

The codes were as follows;

P0190 rail pressure sensor


As the Rail Pressure Sensor is a primary input and sure to place the ECU into reduced performance mode it seemed logical to start here.

A quick KOEO test showed a good 5v supply, a signal of 9.19V and an earth of 4.98V.

Bingo the first problem to solve, I unplugged the sensor hoping the readings would change however they did not. Next I tested the wiring back to the ECU pins, all OK no shorts or open circuits. The problem must be in the ECU! To prove the fault I provided the rail pressure sensor with a temporary earth direct to the battery, the codes cleared.

The ECU registered normal rail pressure during cranking and the engine fired into life.

Then suddenly the engine cut out.

A quick code check now produced;

P0380 Glow Plug/Heater Circuit "A" Malfunction.
P1112 Diesel high pressure monitoring system Malfunction. P1465 A/C Relay circuit malfunction

It was the rail pressure code that caused the engine to cut out.
I cleared the codes and started the engine again, the rail pressure rose as expected during cranking, then settled to around 360 bar then climbed to 400 bar and the engine stalled. The duty cycle of the pressure regulator was fixed at this time and the idle speed constant. So what caused the rail pressure to rise?

Oscilloscope training

Technicians know they need an oscilloscope, accurate diagnosis is often only possible with one.
But is having a scope in the garage enough?
Many technicians who have purchased a automotive scope have not had suitable training in the use of the equipment. This makes using the oscilloscope more difficult when those problem jobs present themselves.
A good example is compression testing, on a modern diesel engine the thought of performing a compression test is at best risky, at worse a nightmare. Removing injectors or glow plugs to access the cylinders can result in hours of frustration or damaged components.
Imagine if this test could be performed in seconds without any parts being removed.
It can using an oscilloscope, some even have programs built into the software to allow quick easy relative compression tests to be carried out.

Civic Type R Idle fault

On the phone this sounded like a simple problem, a Honda Civic Type R has a high idle when cold and is hunting badly when warm.
Got to be an air leak, Right?

The garage has performed a smoke test and no leaks were found in the inlet system. No fault codes are stored in the fault memory and there are no pending codes.

I performed a visual inspection, and everything appeared to be good, the vehicle had a full service history and had just had a service when this fault was mentioned to the garage. The symptoms were just as described on the phone, and once warm the vehicle starting hunting. A quick test ( I placed my hand across the throttle body-the engine stalled immediately) proved the smoke test was right the vehicle had no air leak.

The scan tool showed normal live data, and no DTC's. However the idle speed was not being controlled by the ECU correctly.
If there was a circuit fault there should be a DTC. This could be a mechanical fault with the idle speed control circuit. I removed the throttle body and ISCV this is the rotary type valve on this vehicle and a build up of carbon had resulted in the valve sticking. These valves can be stripped down and cleaned. This was down and the throttle body re-fitted. The idle speed must now be reset using the scan tool, and allowing the engine to idle once warm for 10 minutes.

The vehicle no performed as it should, proving the relying on DTC's is a big problem if the fault is mechanical.

P0420 the most common fault code?

P0420 is possibly the most common DTC retrieved from modern vehicles.
This is because it is one of the codes that is concerned with the exhaust system, any fault upstream of the exhaust can result in a P0420 code.

This why it can be cleared and not return or cleared only to return but not always immediately.
The catalyst can be damaged by many things, but misfire is the most common cause of catalyst damage. P0420 indicates the catalyst is operating below some threshold set within the ECU software. It can be a temporary fault or an indication of catalyst failure.

It is monitored by the O2 sensors, one before the catalyst and one after the catalyst. The two signals are compared and if they are similar the ECU flags the code.

Above is a scan tool image of a catalyst operating efficiently.



There are number of ways to test the catalyst efficiency

• use an infra red thermometer to check for an increase in temperature across the catalyst
• Scan tool data to monitor the switch ratio before and after the catalyst
• oscilloscope to check O2 signal output
• Gas analyser to check readings
• EOBD mode 6

Always test the catalyst under the most favourable conditions, as this is how the ECU tests the catalyst. Hot engine, fast idle/cruise and no other faults present.

The ECU will only monitor the the catalyst efficiency if there are no codes stored. Therefore it is essential to check the catalyst before returning the vehicle to the customer, if a fault has been repaired that may have damaged the catalyst, such as coil pack failure.

Remember it is the O2 sensor that is used to monitor the catalyst so these must be operating correctly.





P0420 Jaguar which bank is bank 1

This a common query with "V" engines the ECU has flagged a code that relates to Bank 1.
However which bank is bank 1?
That's easy, it is the bank that contains cylinder number 1.
So in this case which bank has cylinder number 1 is it the right hand or left hand bank.
Without any technical data, this can become a bit of a puzzle but an easy way to find out is remove the coil pack or injector plug from one of the cylinders, this will flag a code relating to the offending cylinder. That way you can identify cylinder 1 and therefore bank 1. In this case the right hand bank looking from the drivers seat.

But what about the code, what is it trying to tell you?
More on that next time.

P0251 Ford Focus under pressure

This 2003 Ford Focus 1.8TDCi had refused to start one morning, the owner had coaxed it into life with a sniff of easy start.
It had been playing up for a while, under load the glow plug light would flash and the car would loose all performance, now it refuses to start without the help of easy start.

A quick visual check and it looked like the previous garage had thrown some parts at it in an attempt to diagnose the cause. It sported a new fuel filter, new inlet metering valve and a couple of cans of injector cleaner. None of these had cured the fault and the final diagnosis was the high pressure pump.

What had made the garage come to this conclusion?


This code was stored, but after a test drive more codes

These suggest that the rail pressure cannot be controlled within the limits programmed into the ECU. A new fuel metering valve has been fitted so it must be the pump at fault.

Or is it? Rail pressure deviation has a number of causes, and we split them into supply pressure faults, high pressure faults, fuel delivery and return faults.

Using a graphing scan tool it is possible to test the high pressure generation using serial data. The system needs around 200-250 bar before it will switch the injectors.

We had 84 bar cranking, the fuel metering valve can be disconnected on this system and the test repeated and should result in full system pressure (no control) this resulted in 194 bar. We had a high pressure generation fault. But it can not be the metering valve causing the problem.

The scan tool can provide data about fuel delivery and the PID to check is the correction factor for the individual cylinders. Common rail injectors normally have a high return flow rate when they are in trouble so with the excessive correction factor in cylinder 1 we expected the worst when carrying out the back leak test. So it proved, cylinder 1 had twice the return flow of the other injectors.

A new injector was fitted and coded into the ECU. The injector is about 1/10th the price of the pump. But did it fix the pressure fault?

Cranking with the cam sensor disconnected prevents the ECU switching the injectors, and allows the pressure to build in the rail. We now had just over 600 bar cranking.This test proves the pump and low pressure stage as any faults would not generate such high pressures.

Losing Focus

This looked like a simple diagnosis.

A 2005 Ford focus1.6TDCI with the MIL light on, and black smoke coming from the exhaust during hard acceleration.

First we performed a visual inspection and noticed a new Air mass meter(AMM). The test drive proved the customer was right, black smoke and poor vehicle performance.

Time to attach the code reader.

P1101 was the code stored. This relates to the air mass meter out of self test range.
possible causes for this code include;
Low Battery Voltage
AMM partially connected
AMM contaminated
Ground or power supply problems
AMM open circuit to ECU
AMM damaged
ECU damage

But as the component is new, and the customer will be less than pleased if the diagnosis is the same as a few months ago, and the light comes back on with the same symptoms. The pressure is now on. What is causing the AMM to under read, a classic cause and effect diagnostic problem. The previous garage has fixed the effect, and the problem has returned, we need to establish the cause.

This is where information can help, the diagnostic triangle consists of three elements, equipment, information and knowledge. All three are required to diagnose vehicles effectively.



We discovered that the problem can be caused by the crankcase breather pipe contaminating the AMM, and ford has modified the pipe to help prevent the problem returning. They also reprogram the ECU with larger performance parameters to prevent the MIL illuminating.


I checked the software number and the vehicle needed the software upgrades, along with the modified pipe. However the AMM was now contaminated, as it was still relatively new I cleaned it with brake cleaner and hoped for the best. On test drive the vehicle performed as it should, and there was no evidence of the black smoke. Satisfied we had found the cause, the car was returned to the customer.

Out of Ranger

A Ford Ranger had turned up at a garage overnight, with the keys posted through the letter box and a note asking if the garage could get it going.

The problem here is not fixing the vehicle but a lack of information.

1, how did the fault occur
2, when did it happen
3, with which key(s)
4, how much are you willing to spend

The customer was contacted and answered all the questions, but fustrated at the lack of diagnosis, surely you can just plug it in and find out what's wrong?

The garage did not have the diagnostic plug to tackle the job and asked if I could have a look. I found a code stored P1649 pump control module malfunction.

After a quick check of the supply and grounds this looked like a ECU fault.
The module was removed and sent away for repair, it was repaired but the vehicle still would not start. Next step was to check the engine ECU, a separate ECU that shares inputs and outputs with the pump control module. This too appeared to be in trouble. So this was sent away for testing and repairs.

What had caused the damage to both control units and is the problem going to destroy the repaired units?

Further testing didn't show any problems. The customer told us upon collection he had tried jump starting the vehicle when it refused to start, and thinks he may have got the leads the wrong way round!

VW EPC Light

I often get asked why the EPC light can be illuminated without the MIL light.

EPC -electronic power control consists of the pedal position sensors, MAF sensor, ECU, and throttle valve.
A classic input - logic -output system.
The ECU (ME7) has a torque based architecture, that is to say it manages outputs based on torque demands of the driver and the vehicle systems.

One of these outputs is the throttle valve.

If a fault occurs in the throttle valve, ECU or wiring, the ECU defaults into a limp home mode.
The Electronic Power Control (EPC) light will illuminate.

Depending on the fault one of three modes can be selected.

Mode 1
If one throttle position sensor fails, torque output is reduced.

The customer may complain of a lack of power.
This mode requires one functional throttle position sensor with an intact signal, and
engine load readings from the Mass Air Flow (MAF) sensor.

Mode 2
If the throttle valve actuator fails or malfunctions, the voltage to it is shut off and the
throttle valve defaults to its emergency running position. Torque requests are executed via ignition and charge pressure regulation. As a result, the engine will show very little
response to the throttle. This mode requires signals from both throttle position sensors.

Mode 3
If the throttle valve position sensor fails (implausible signals), the voltage to it is shut off and the throttle valve goes to its emergency running position. The engine speed is limited to 1200
RPM by restricting the fuel injector pulse width and ignition timing.

Therefore a technician can predict the fault from observing which limp home mode has been selected. As the engine continues to run correctly, there is no excessive emissions and therefore no MIL.

Vaux Pop P1120 P1550

This 2001 Zafira (engine code Z18XE) came from another garage, who had extracted the fault codes. The codes were P1120 (Accelerator Pedal Position Sensor 1 Low Input)
and P1550 (Electronic Throttle Control Reduced Power)
They looked at the live data and pedal position sensor 1 did not respond to the pedal movement.
So it looked like a simple sensor fault, but another garage had replaced the pedal box containing the sensors and the fault remained. They had also removed and cleaned the throttle, and could not perform the throttle re-learn using their diagnostic tool.
Due to the cost of the repairs so far, they asked for a second opinion.
As always we started with a visual inspection. Then confirmed the fault, poor performance, stalling and MIL on. Then we looked for fault codes in all modules as the TCS light was also flashing.
The same codes were presented in the engine control module.
This is where system knowledge is a key ingredient to your diagnostic routine.
P1550 is stored as a result of the P1120 code, it is a symptom not a cause. The ECU has gone into a safe mode of operation. (reduced power mode).
So what could be the cause of the pedal position sensor 1 low input?
The list includes, wiring faults, sensor faults, Module faults. How to work out which one is the cause requires some information. Using a wiring diagram we are able to determine which ECU pins were supplies, earths and signals. A multi-meter could then be used to test the wiring, we elected to test at the ECU. This allows you to test the entire circuit at once.
The supplies and earths were good, and both sensors appeared to be working. One sensor output is twice the other.
This means the fault is inside the ECU. Not uncommon with this engine.
Now the customer is left with a choice, new ECU and coding at the Vauxhall dealers, or a refurbished second unit. The customer sourced his own ECU and it came with the transponder and key chips. Once fitted it required no coding, other than a throttle reset which was carried out using the original repairers equipment.

Feeling Cranky?

We were called to look at a race car that had a Ford Cosworth V6 engine fitted in place of the original Essex V6. This conversion should in theory free up 50-60 bhp, however the engine would not fire.

This engine ran the old Ford EDIS ignition set up, with a separate ecu providing the fuel.

The fuel ecu modifies the ignition timing after receiving a digital signal from the EDIS module. It uses this signal for its speed/position reference.

As there was no fuel or spark it seemed logical to start with this signal. But only after checking for the correct lives and earths at both ecus. We corrected a number of wiring errors, and thought we might have sorted the problem. But it still refused to fire up.

We checked for the PIP signal.

PIP is the Ford term for the speed/position reference signal (profile ignition pickup).

There was no output from the EDIS. Next step is to check the input.

This is a simple inductive crank sensor from the front pulley. There was a signal, however it was different from the expected signal. We suspected the crank sensor was the culprit. A quick resistance check showed a normal 0.8K ohms, this is why an oscilloscope is essential, if we had just used a meter, we would have an AC frequency and the correct resistance readings. This would then suggest a fault with the EDIS module.

Input - logic- Output model would lead to miss diagnosis of the module as there was no output despite the correct power, ground and inputs.

Unable to find a replacement sensor on the self we rigged up a CKS from a Renault using a cable tie and two jumper wires. result is shown below.

The yellow trace is the CKS and the green trace the PIP.

The ECU was now injecting and the coil pack sparking. The difference between the two CKS traces is the waveform around the missing tooth. The jump in the waveform is due to the spark plugs being out of the engine causing RFi made worse by the exposed makeshift CKS wiring.

Another successful diagnosis due to the oscilloscope being able to display the full picture.