C5 X7 P1166 Diagnosis & Repair

[steveclv]

So the time has come to work out what is wrong with my 2009 C5 X7 (2L 138) that keeps throwing a P1166 code that puts it into a limp (ish) mode every time I use kickdown to overtake.

Can anyone give me an idea where to start please?

Is it too high or too low a pressure?

Should I start with the HP fuel pump or is there a Fuel Pressure Regulator somewhere?

Manny thanks

[RichardW]

Have you changed the fuel filter?

[GiveMeABreak]

There's a known fault for this engine (DW10BTED4) with any of the following codes present: P0088, P1166, P0181 or P0183):

Symptoms are a flat spot on acceleration, or the engine stalling, unstable idle speed or hesitation (particularly when cold with engine speed between idle and 2000 RPM).

Action is to replace the high pressure fuel pump pressure regulator where necessary.

A dealership with Diagbox would confirm by the following checks. You seem to have Diagbox, so just run some live tests of the engine ECU and look specifically to find the 'measured fuel pressure' parameter or choose customised parameters and select it yourself. It should provide the output in the form of a live graph for you as the engine is running. Compare to the chart below:

"A": Signal conforms.
"B": Signal does not conform (Significant fluctuation).

• Start the engine and let it run at idle.
• Check the "Measured fuel pressure" signal using the diagnostic tool:
• If the signal fluctuates significantly (Fuel pressure unstable) (Figure "B"), replace the high pressure fuel pressure regulator.
• If the signal does not fluctuate significantly (Fuel pressure stable) (Figure "A") do not replace, but continue with other diagnosis.
  
  There should be any other codes apart from one or more of those listed above present (apart for the common glow plug faults), so deal with any other faults first.

[steveclv]

Brill - thanks (yes, it has a brand new Bosch diesel filter and yes I have Diagbox)

I'll run the tests to see what I can see.

Is there a procedure for replacement and part number for the pressure regulator?

There are no other errors apart from the usual ones (suspension, cruise control, bsi) that occur when it goes innto limp mode.

Many thanks

[GiveMeABreak]

(1) Regulator, part: 193339, £215.41

Let me know when you are nearer to replacing it and I'll put a guide together.

[steveclv]

Awesome! Thanks

[steveclv]

So just back from my trip to the UK - 3,700km (2,300 miles) at an average speed of 46mph and 45mpg - very happy. I was doing even better until I got to the French motorways where driving at the 130km/hr (ish lol) took a hit on the fuel consumption
She ran (almost) perfectly - I avoided any further P1166 errors by keeping away from kickdown and the only other error was the cruise control kicking off when I had it set at 45mph and then accelerated up to 80mph without disengaging it - it disengaged itself and then refused to operate again until I stopped and restarted the engine - then it was fine.
The only other issue was a blown headlamp bulb
I love this car

I have ordered a new fuel pressure regulator from Aliexpress for £35 - on the basis that most of the stuff is probably made in China these days - worth a try anyway. If that doesn't fix it then I'll likely change out the high pressure fuel pump.

[GiveMeABreak]

I hate to say it but I strongly suggest you avoid that place for sensors - cheap for a reason. I always recommend getting a branded sensor - there are plenty cheaper than the OEM version. Have a look here:

https://www.autodoc.co.uk/car-parts/oem/193339

[aerodynamica]

I'm reading this with interest because I think I have the same issue.

I only got the same error code after it went into limp mode putting the foot down with the cruise on. It only cleared after performing the recommended 'full throttle for several seconds " then off when on the motorway and repeat. But I now have an annoying hesitation moving off from stationary when cold. Been like it for ages but only today it seems worse.

[steveclv]

Aero - I'm leading towards the sensor but I also have a weeping oil seal on the HP fuel pump so I'm toying between replacing the sensor and replacing the HP pump as well. Have you checked your error code yet?

Marc - yes, I know what you mean but so much stuff is made in China these days and the low cost EU versions seem to have just as many negative reviews. It's also hard to be sure where some of the famous Brands manufacture these days

[GiveMeABreak]

No worries - just be aware these can often be DOA.

[aerodynamica]

Aero - I'm leading towards the sensor but I also have a weeping oil seal on the HP fuel pump so I'm toying between replacing the sensor and replacing the HP pump as well. Have you checked your error code yet?

Marc - yes, I know what you mean but so much stuff is made in China these days and the low cost EU versions seem to have just as many negative reviews. It's also hard to be sure where some of the famous Brands manufacture these days

I had this same fault code, I'm thinking that this part is fairly accessible and easy to replace (unless it involves any calibrating and resetting and talking to the BSI and such) So thought I'd concentrate on that. Where are you seeing the seal leaking ?

[aerodynamica]

I hate to say it but I strongly suggest you avoid that place for sensors - cheap for a reason. I always recommend getting a branded sensor - there are plenty cheaper than the OEM version. Have a look here:

https://www.autodoc.co.uk/car-parts/oem/193339

Quite a range of prices for those sensors. Do you think the costlier ones are the only real choice?

[GiveMeABreak]

Personally, I’d only get a ‘known’ brand as sensors are so important to the overall system. The number of people that have had duff ones from the likes of ECP and other unheard of makes with little feedback over the years is significant enough that I would only get something of a good quality.

If these are anything like the knock-off car bulb fakes that are prolific on well known shopping sites, then that’s another thing to watch for.

I only ever shopped on authorised reseller websites when buying Xenon bulbs for previous cars that could be verified for piece of mind. There’s more and more fake products being copied on Amazon now, especially since they’ve opened the floodgates to more Chinese sellers.

Fake hard drives that have been altered to state a higher capacity than they are to fool people, fake SSDs, fake razor blades fake Philips toothbrush heads, fake electrical goods - it’s a nightmare and getting worse.

[steveclv]

Where are you seeing the seal leaking ?

I found some oil staining on the bottom of my auto gearbox and determined it was engine oil - so with the undertray removed, looking up towards the HP fuel pump with a torch, there is an electrical connector underneath the pump that was wet with oil and the only place that could come from was the HP fuel pump seal where it mounts to the engine. A reasonably well known issue.
It's not bad enough to create drips on the floor but just one of those jobs that need doing