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.