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!