Intermittent fault

K

Krister

Member
In my ever continuing hunt for an odd fault on my 1.4 petrol I've finally managed to get the following fault code using VCDS lite:

>>>>>>
Control Module Part Number: 036 906 034 Q
Component and/or Version: MARELLI 4LV 3720
Software Coding: 00051
Work Shop Code: WSC 02138
Additional Info: WAUZZZ8ZZ1N034323 AUZ7Z0Y1669105
1 Fault Found:
17961 - Barometric / Manifold Pressure Signals: Implausible Correlation
P1553 - 35-10 - - - Intermittent
>>>>>>

The issue I have is that when the engine is warmed up a bit, driving with light load the EPC comes on and most of the times also anti-skid and ABS fault. Previously it hasn't recorded any fault codes on the engine, only ABS, but I finally caught the above. I never get any faults when chugging along at motorway speeds.

Done so far:
Cleaned and adapted the throttle.
Replaced the Lambda control probe.
Checked the function of the cannister valve.
Checked spark plugs.
Cleaned the EGR valve.

Is there a pressure sensor on the intake and if so, where is it located?
Any ideas are most welcome, the garage is booked for the next few weeks so there's time to fiddle...
 
Sorry to hear of your problems

I've just had a look at my manifold and see theres an electronic module on the inlet manifold at the opposite end to the throttle body. The part number is 036906051 and appears to be a pressure sensor.

I've had a complete engine replacement so the one I have is surplus to requirements. If you want it drop me a personal message.

I guess the ESP and ABS require a measured value for vacume in the inlet manifold as the brake servo is directly connected to the inlet manifold.

Best of luck

Malcolm
 
Thanks, I found the sensor too after looking through the ETKA files. I'll pull it off and see if there's anything apparently wrong.
 
The only other fault I've managed to squeeze out of it that makes any sense at all is:

2 Faults Found:
17961 - Barometric / Manifold Pressure Signals: Implausible Correlation
P1553 - 35-10 - - - Intermittent
17912 - Intake Air System: Leak Detected
P1504 - 35-10 - - - Intermittent

This after driving slowly and with low load. If I drive it hard, accelerate, drive fast or let it idle for that matter, I don't get this fault. I'm leaning towards a bad MAP sensor, but it could be a leak in the system somewhere. Usually, the codes I get are:

Address 03: ABS Brakes Labels: Redir Fail!
Controller: 8Z0 907 379 B
Component: ESP 20 CAN V015
Coding: 10758
Shop #: WSC 00000
1 Fault Found:
01314 - Engine Control Module
79-10 - Please Check Fault Codes - Intermittent

Which doesn't help a great deal, but, with patience I've managed the top scores also...
Tricky pieces of machinery these modern cars, everything needs to be on the mark for it to be happy...

My current plan of attack is to ensure that the manifold doesn't have any leaks. There aren't too many options for air to enter the manifold, it's either the throttle, EGR or coal cannister, including the seals between the throttle body and manifold itself and the associated plumbing. Next would be a 65 EUR replacement of the MAP sensor itself. If that doesn't work then I think I may have a glitchy ECU or wiring. But, considering that the fault seems to occur at a fairly constant condition, I think electrical fault is out, the sensor sounds more reasonable somehow.

But, I'm just an amateur...
 
At least I am not alone, it sounds very similar to my combination of codes and symptoms.

As I had damp problems I was thinking wiring or connector problems, but dried everything out and checked all connections, nothing seems to change.
 
So, does your car drive bad at low loads? If I play with it, I can get it to jolt and lurch at low engine loads, it gets so bad I think my teeth are gonna fall out. But, if I accelerate hard it doesn't happen. It runs fine up to redline.

How does your car behave when you drive it around?
 
When the engine is cold it runs fine, also at speed no issues,

But after the engine has been running a while, can jolt and lurch a bit when you pull from a junction.

Revs occasionally a bit erratically when ticking over.
 
That's exactly what mine does! Ok, so that's comforting, in a sense...
What have you done so far in terms of fault searching?
 
I found a hole in a ducting tube I replaced the tube, checked today and this code has not come back:

17961 - Barometric / Manifold Pressure Signals: Implausible Correlation
P1553 - 35-10 - - - Intermittent

The tube replaced is about 15 cm long and 45mm dia and passes above the alternator.

Still getting the warning lights so probably not related.

Correction : came back a few days later :(
 
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Y're talking about the intake tube from the air filter to the throttle? From what I can gather, a leak there shouldn't actually cause a fault, it's not great, but not really an issue (tho I could be wrong). I tried pulling the crankcase vent line from the intake and it didn't seem to affect anything.

I've also replaced the MAP sensor which was really dirty, or oily rather. But, that didn't do anything.

From reading on other forums, VW, Seat, Skoda etc. the EPC light basically just says "something's wrong". A scan should help but in my case all it says is that there's an intermittend fault with the ECU. And, from these forums, it could be anything mounted on the car that's failing apparently. Very useful diagnostic tool....

Anyway, my car behaves the same still. I'll keep searching for leaks unless someone can come up with another idea... Perhaps I ruined something when I cleaned the throttle body? Who knows.
 
Thanks for the tip Sarge, I read that piece the other day!

Not meaning to be impolite but the item you refer to as the MAP sensor is in fact a heater tube (check the parts catalogue, ETKA). I think it's meant to keep the crankcase vent ice-free and possibly heat the intake/throttle a little.
The MAP sits on the side of the intake manifold, to the right in your picture and below the fuel lines.

In any case, I felt that same tube that you're mentioning and it's slightly worn where it makes contact with the brake line as you say, however, if it were the cause of the problem I would think that when I pull the tube clear off I would have massive trouble. But, nothing happens.

Spent a few hours this evening provoking my poor car into epileptic behaviour. I've noticed that by pulling the tube from the coal cannister that sits between the valve and the throttle, I can replicate the fault conditions. I've had the valve out and tested it (seems to work) but I'm beginning to think that this is where the problem lies after all.
Had a thought about low voltage causing these problems but my battery holds 13.5V power off, and over 15 with the engine running. A bit high in my mind but perhaps the longer leads from the boot require this higher voltage.

Then again, I've been wrong about my assumptions so far...
 
Update in case anyone else has trouble.

My problems as described earlier:
- jolts and lurches and lights up EPC, brake and anti-skid when pulling away or sometimes while driving at part throttle.
- runs fine at idle and at speed (motorway) and also revs fine when parked.

fault code:
17961 - Barometric / Manifold Pressure Signals: Implausible Correlation

Done so far:
- replaced broadband lamba probe
- replaced MAP sensor
- cleaned throttle and re adapted
- cleaned and checked EGR for function and flow
- checked active coal cannister function/valve function
- pressure tested the intake system
- checked valve timing
- checked catalyst for blockage
- checked intake for blockage

No change

Finally checked compression:
cylinder 1 - 14 kg
cylinder 2 - 14 kg
cylinder 3 - 13,5 kg
cylinder 4 - 12,5 kg

Likely problem is either broken piston ring or if I'm lucky, valve guide or seal...
Sometimes, the problem is the engine after all and it looks like it in this case.
The logic being, because the number 4 cylinder leaks it is not creating the vacuum it should. This tells the computer that the pressure in the intake is not a reasonable value given the throttle position and RPM. On idle it is within limits, and at open throttle settings as well. The part throttle condition creates the greatest vacuum so it is more sensitive.

Any other ideas?
 
Have you replaced or just cleaned the egr, the only reason I ask is you said when you rev the engine or drive at speed the fault does not occur, but at these conditions the egr would switch off, I could be mistaken. But both me and my wife with previous cars have had issues with the egr which lead to loads of fault codes.

Alan
 
Nope, not replaced. It's in a workshop at the moment and they've checked the operation of the valve and made sure nothing is clogged or anything. I suspected the EGR after doing my initial tests at home, but at the moment it doesn't seem to be at fault.
 
- thread resurrection -

We have very similar problems with our 1.4 petrol A2, any more news on this issue anyone? :)
 
hi everybody,

the problems and error codes you describe are very close to mine.

as you actually did a compression check on your cyliders, it made me curious to something...

have any of you checked the the timing belt for cams out alignment or damage to the tentioner or cam and/or crank sensor? also cam chain adjuster on the opposite side of head?
sounds like maybe the one of the camshafts is off timing creating very similar symptoms (only needs a couple of mm from perfect sync). just trying to look at this from a mechanical view, since electical wires and sensors seem to be replaced by many of us

- Chris
 
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geneva-a2 said:
When the engine is cold it runs fine, also at speed no issues,

But after the engine has been running a while, can jolt and lurch a bit when you pull from a junction.

Revs occasionally a bit erratically when ticking over.
Click to expand...

I had the same on my 2001 petrol when I first bought the car. Replaced the plugs, plug leads and coil pack which helped a little. The best improvement was when I used WYNNS fuel injector cleaner in a half full tank of gas plus some 98RON fuel. This has made it much better leading me to think that lots of short school run journeys had clogged up the injectors. So far, so good so keeping my fingers crossed that this is the solution!!! :cool:
 
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