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ECU fault? Help please
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ChrisW   
Sat May 08 2021, 10:39am
Joined: Jun 18 2013
Member No: #1335
Location: Surrey
 My 2008 2.7HDI Lignage (80,000 mileage) is playing up in a strange way and I'd very much appreciate any advice before I take it into the main dealer.

A couple of months ago I found I could not change the dashboard display screen. Previously I could use the menu button to scroll through various displays but it was locked on the screen showing engine temperature and tyre pressure warnings.

Now the car repeatedly goes into limp mode with various turbo warnings (wastegate solenoid A and/or B; overboost; underboost). Previously I would occasionally get an overboost warning and limp when accelerating hard uphill, which I attributed to sticky turbo vanes or wastegate. This would reset ok when the engine was stopped and restarted. But now the car goes into limp mode with turbo warnings about 10 seconds after start-up even when it is just idling, before it has even been driven. It still drives but only in limp mode.

I have checked the readout from the boost sensor, taken from the diagnostic socket, and it is fine and goes up and down as expected with the engine load, so I don't think the boost sensor is the problem. I don't have a Lexia, only an Ancel code reader which reads the codes and can delete them. It has a live display showing manifold air pressure, etc when the car is driven.

I thought it might be a computer fault, so disconnected the earth from the battery and left it for a few hours before reconnecting (the typical switch it off and switch it on again advice). This hasn't fixed it. The display screen is now frozen on the day and date screen and I cannot change the date from January 2003. Still limp mode.

Any ideas or suggestions much appreciated. Is there an ECU that controls both the display screen and turbo that might explain faults on both these systems?
arconell3   
Sun May 09 2021, 01:41pm
Joined: Jun 28 2012
Member No: #922
Location: Kalkar
 First of all, I don't think your problems are caused by any of the 26 ECU's in your car. They almost invariabley signal a problem because there is a problem, not because the ECU is faulty. That is one of the functions they were designed for! Your problems occur independently of each other, unless there is a low voltage condition, in which case you'll get a whole laundry list of faults from all ECU's.

As for the turboboost problem, there are a number of things you can easily check on the air intake tract. That includes the MAP sensor inside the butterfly housing and both MAF sensors attached to the air filter housing. Start cleaning all 3 sensors, using isopropanol (don't use brake cleaner!) and see what happens. Also check the connections of the bridge (airduct between the 2 turbos, running across the engine). While you are at it, also clean the whole butterfly housing, you will probably find it pretty much clogged up.

Good luck,

Robert
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ChrisW   
Sat May 15 2021, 11:37am
Joined: Jun 18 2013
Member No: #1335
Location: Surrey
 Hi Robert. Thank you for your reply, which is very helpful. I will do the checks you suggest.

You are right, it's nothing to do with the ECUs. I am now pretty sure that the root cause is sticking turbo vanes caused by carbon build-up. I added two bottles of Forte turbo cleaner to half a tank. I then drove it repeatedly (20+ times!) up a fairly steep hill, causing it to go into limp mode each time. I think things are now getting better. I no longer get overboost warnings but still get wastegate warnings when accelerating hard.

I think the turbo vanes can now move sufficiently to prevent overboost but are still sticky. I think this causes the wastegate warning and limp when accelerating hard because the sticky vane causes the solenoid to take too much current, which triggers the warning.

I will continue with the turbo cleaners to see if this fixes the problem completely in time. At least the car is now driving fine as long as I accelerate gently.
 

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