C5 2 litre Hdi power loss -still not resolved.

[Paul-R]

It's a bit like the old idea of catching a bird by putting salt on its tail.

Ahhh, the old Cerebos advert.

[myglaren]

are the Bosch and Siemens interchangeable? Ie. Could I put a Siemens in if the one already in the car is a Bosch?

Pass on that one. If you have one there, try it and see.

[boristhespie]

Haven't bought it yet. Wouldn't want to get the wrong obe.

[myglaren]

It is simplicity itself to remove the one fitted and check the make and series.
You are possibly looking at the same one that I was and there was a discrepancy on the type number - only one character/digit but I thought that if it was unsuitable it was less hassle to pop down to the dealers and buy one over the counter.
As it turned out is wasn't that simple but the option to easily change an incorrect part appealed to me.

[Paul-R]

I checked the old one that I replaced last year it was a Siemens one. The replacement was a motor factors' one and therefore no-name...

[centurus2400]

[quote="centurus2400"]If I unplug the MAF it immediately brings on the MIL light and the dreaded 'antipollution fault' appears on the LCD screen.

The engine will run, but it's in limp home mode andt I assume the ECU has switched to some generic built in airflow values rather than measuring actual values.


Oops, I didn't make myself very clear here- the limp home mode is only active while the MAF is unplugged. Reconnect it and the MIL light goes out after, I think, 5 starts and the engine goes out of limp home mode immediately.

The next step is to remove the MAF and examine it - maybe even try carb cleaner and/or a cotton bud. I know they're delicate things and I don't want to damage it, but I want to see if it makes any difference at all.

[cachaciero]

Mini Tutorial aka sensors and warning messages.

It needs to be born in mind that for the most part the ECU's have the ability to detect the presence (or not!) of most sensors which is different to their ability to detect errors from those sensors.

The ECU when it powers up will do an initialisation and check routine part of which will be checking sensor lines for a sensible input, often this may be no more than "are the inputs open circuit or short circuit" but could be a bit more precise than that.
Having done it's initialisation bit it will then start to crunch the numbers based upon data from all the sensors if at some point some of the data is inconsistent it will post an error related to the most likely component based upon the numbers.

Now as regards errors the ECU classifies errors as potentially engine damaging or not and both of these cases can be temporary or permanent.
Temporary means that it has happened but the error is no longer there after re-starting the engine and permanent means that the problem is still present after shutting down (and by implication resetting the logic) and re-starting.
For such errors the logic will maintain the warning for as I recall three engine start and run sequences, the engine has to run for a certain time with no re-appearance of the fault after which the warning will be extinguished BUT the fault will still be recorded in the ECU.
Those errors which are potentially engine damaging e.g. Turbo Overboost work exactly the same way except that they also limit engine power to something in the region of 2K revs.

From this you can see that if for example you have a Turbo Overboost condition the ECU will go into LIMP mode and post a message. Now if you shutdown and re-start the Turbo Overboost not being present at idle the engine will not go into limp mode but it will still put the warning up.
If you now drive the car, for as long as you don't overboost it you will have the full rev range available, after three start run cycles without overboost occuring the warning light will go out. N.B This is a common scenario on the 2.2 with a defective swirl valve actuator.

If as a way of trying to defeat the system you disconnect the Turbo pressure sensor then as soon as you start the car the ECU "knows" the sensor is absent and will post a warning and lock you down to LIMP mode.
Equally with the MAF you can run the engine without the MAF connected but you will have a permanent warning up and my guess is that the ECU will not execute code that uses the MAF so any results will not be very conclusive.
More informative is to take the MAF out of the air circuit which based upon my experience will give you very poor performance i.e if you do that and notice no difference then the MAF is probably shot if you do it and notice a big performance drop then the MAF is probably o.k

cachaciero

[RichardW]

There's only one part that covers Siemens and Bosch and 2.2 HDi as well:

Part Number Description Quantity Price excl. VAT Price incl. VAT Total incl. VAT


00001920AG AIR METRG DEVIC 110.36 GBP 132.43 GBP 132.43 GBP

[centurus2400]

More informative is to take the MAF out of the air circuit which based upon my experience will give you very poor performance i.e if you do that and notice no difference then the MAF is probably shot if you do it and notice a big performance drop then the MAF is probably o.k

cachaciero

That's the thing. The performance of the car is pretty poor, but the MIL isn't lit, there are no fault codes appearing on a Lexia, and the live data seems to be OK as well.

What you're saying is to leave to MAF connected but removed from the inlet pipe and then see if there's a difference - I'll see how easy that is to arrange and give it a try. I'm pretty sure the performance, such as it is, will drop even further.


Of course if the turbo system and MAF are OK I'm not really sure what to do next.

[cachaciero]

Easy enough to take the MAF out of the air circuit just unclip the rubber pipe between it and the next plastic bit, o.k so you run without air cleaner but that's o.k to prove the point.

cachaciero

[cachaciero]

If the performance is poor and no MIL that implies that the ECU logic believes all is well I wonder if it is possible to have two sensor faults that effectively cancel each other out as far as ECU warnings are concerned, just idle speculation

cachaciero

[myglaren]

The next step is to remove the MAF and examine it - maybe even try carb cleaner and/or a cotton bud. I know they're delicate things and I don't want to damage it, but I want to see if it makes any difference at all.

Don't use a cotton wool bud - just spray with carb cleaner and let it soak a while then repeat a few times.

I tested my defunct one with a cotton wool bud and some meths - platinum wire disappeared at the slightest touch.

[3CV]

I wonder if I may add the problem with my 2006 C5 TDi to this thread?

It starts normally but only after a few seconds the throttle has no effect on RPM. I had the car towed to a service centre well accredited with European cars and they ran the diagnostics. Nothing showed faulty but they disconnected the throttle cleaned all the contacts, test drove it and it appeared to be fine.
We drove it home without any problems but it did exactly the same this morning after driving it out of the garage at home for the first time since driving home. This time I noticed that while the car was idling the revs dropped and it struggled until it stalled despite trying to maintain the revs.
What is the MAP and does anyone recognise the problem I have described?

[boristhespie]

So the lexia could say open or short curcuit.

Which on is a fault state
Then?

I am assuming that's the shortq curcuit?

I have a couple of short curcuits showing up.

My other car is not in limp mode, it just doesn't have any power and takes forever to get any speed and dies on long shallow hills. The engine management light is on.

Also the other car for me the lexia says there is a fault with airflow but the garage said they blocked egr, tried another MAF and i have no heards any hiss anywhere which may indicate a leak.

This loss of power seems common though but frustrating to identify and sort.

[myglaren]

Welcome 3CV.
It could still be the throttle potentiometer, the wiper could be dirty or burned. Cleaning the external contacts wouldn't affect that.

It is possible to clean the wiper but is a destructive process that gives a short term improvement but eventually leads to complete failure. Only useful to eliminate symptoms and means you need a new potentiometer anyway.

The MAF is the Mass Air Flow sensor.
The MAP is the Manifold Air Pressure sensor.
MAPS are usually located in the inlet manifold - hence the name. On the C5 it is on a small extension to the boost pipe/hose where it comes out of the intercooler. Easy to access.

It is a possibility that the place that read the codes don't have a Lexia diagnostic computer and didn't have access to data that would have been more accurate and useful.