Ma' Beloved AUDI A4 - Engine Management Light not working

[caradvice]

Hiya,

I have a beloved AUDI A4 TDI 1.9 (B6 96KW 2001)

The dashboard Check Engine/MIL/ECU light is not turning on when it should be.

They have made this light a requirement for UK MOT tests this year (oh gawd).

Main Issue:
• No ECU light on and off when ignition
• No ECU light when engine sensors are deliberately tampered with (e.g. MAF)

Had a diagnostic recently done:
• Car engine is running fine
• ECU communicates with diagnostic tool
• ECU logs any fault codes correctly (e.g. MAF tampering)
• I thus assume the ECU work okay (engine running fine)
• Cluster ECU Check engine light was tested OK via diagnostic tool
• I assume the cluster is okay as the bulb can be switched on and off

How would I start to get someone to diagnose this and fix the issue?

I understand the immobiliser network has three elements - the ignition, ECU and dash cluster? If each of the elements in this group is working individually, should I conclude there something broken between the ECU to dash cluster which is preventing the light from turning on and off for ignition (or when the engine sensors are deliberately messed with)??

Could it be a wire, a seating, a pin connector? How can I diagnose this issue and where would be the right area of focus?

Welcome any advice or questions.

[A41.8TB6]

I swear I read it somewhere about someone is having ECU problem and the CEL isn't lighting up. BTW have u tried disconnecting your battery to clear everything up.

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[caradvice]

I swear I read it somewhere about someone is having ECU problem and the CEL isn't lighting up. BTW have u tried disconnecting your battery to clear everything up.

Hi, thanks - can try that. Disconnect the black terminal I guess and then leave for 15mins? - I assume that is enough time to discharge. Good suggestion.

The glow plug lights (its a TDI) is coming on and off on ignition - and therefore the connection from the ECU to the Instrument Cluster must be working? Just the Check-engine light thing not coming on.

Also assume that if there was a connection issue from the ECU to the instrument cluster - the light would come on and stay on? - and there would be code stored in the ECU? (which I am being told there is not).

[A41.8TB6]

Sometimes the traditional scanner or off the shelf type won't see it like vagcom will. I have that experience that it doesn't show in the scanner but will leave a code in vagcom.

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[caradvice]

Yup, am learning lots of different OBD2 scanners. The garages in the UK use seem to use a large Delphi Scanner which is something generic used for all makes. I took it too a specialist and the VAGCOM could read the codes okay - so the link to the ECU or the ECU itself is clearly not broken.

Tried taking the negative terminal of the battery out for 30mins and then put it back. Nothing changed - other than the ABS light (which should go off with a bit of driving). ECU light still not coming on and off with ignition.

So, have bought a Torx 25 and will try taking the cluster out of the dash and see if messing with the harness will make some difference - I don't think it will somehow.

Next step may be to ship the cluster to one of these type of companies that will probably do a repair. But its not cheap and who knows if it is indeed the cluster, else I will be wasting my time.

The Cluster repair companies are saying, that it probably "is" the cluster, else the light would come on and stay with fault codes if it was anything else or the cluster. But is always only the cluster, if the light does not come on (if you get the logic).

[hightime80]

If the ecu has no stored faults then it has to be the cluster...so one would think.

[Ol Dirty Noodle]

Ummm not to sound like a dick but maybe the bulb itself is out and everything else is working fine???

[caradvice]

Ummm not to sound like a dick but maybe the bulb itself is out and everything else is working fine???

Thought it could be as well - but the VAG COM garage said they did some instrument check as part of diagnostic and the ECU light came on the Cluster as part of the check- so that bulb must be working (and I don't think they break very often in anycase).

[Ol Dirty Noodle]

Thought it could be as well - but the VAG COM garage said they did some instrument check as part of diagnostic and the ECU light came on the Cluster as part of the check- so that bulb must be working (and I don't think they break very often in anycase).

Hmmm that’s interesting I must’ve missed that, in that case why not try having the ecu reflashed with a stock bin and having the cluster reset to what ever extent your shop can, the fact that it came on with the test makes this more difficult to diagnose

[Human Garbage]

You sure your ECU hasn't been remapped? Some shoddy tuners just disable setting DTCs to cover the fact they can't tune.

[caradvice]

Could be, but before I had the car, had the car 10yrs and trying to recall ever seeing that light on ever. Had engine problems very occasionally but no light.

The consensus from the mechanics is that it is cluster issue, apparently they have seen it on these cars. The glow plug light is coming on and off, therefore there must be comms between the ecu and cluster, so why isn't the check engine light not coming on and off?

Think there is going to be a lot more of these issues fun the UK as the government are getting stricter on the MOT vehicle tests.

Cluster fix may cost about £120, and no guarantees that it will fix it. Have to pull cluster out and send it to a dash repair company. Of course no car whilst they fix it. Not sure it's worth it, instead I could just buy an OBD2 reader and keep on eye on the car should there be issues.

[EuroxS4]

id would be looking at wiring.I would check to see if any faults are stored.I had allroad sometime ago that came into the shop.Some asshole put black electrical tape over the led under the gauge faces.The light never came on.LOL it had alot of faults.if you know for a fact that the light works.I would be looking for a loose connection in the wiring or a issue with the ecu.

[caradvice]

id would be looking at wiring.I would check to see if any faults are stored.I had allroad sometime ago that came into the shop.Some asshole put black electrical tape over the led under the gauge faces.The light never came on.LOL it had alot of faults.if you know for a fact that the light works.I would be looking for a loose connection in the wiring or a issue with the ecu.

Yup, first thing we checked - the LED on the Check-engine light had been masked. It lights up with an instrument test via the OBD2 scanner, so no issues with the light. Then we thought its the comms between the ECU and the dash (something to do with K-line?), but.... the glow plug light is coming on and off with ignition and the mechanic guy is puzzled because if there was a permanent break in that connection then the ECU would not switch on/off the glow plug light on ignition. And also there would be fault codes in the ECU with it not being able to connect to the dash cluster (so I am told).

We are thus assuming a dash issue and something to do with the hardware/software cirucuit boards etc in the cluster? These kinds of shops fix them - http://www.clusterrepairsuk.co.uk/. But would hate to spend the £120 odd pounds on a sending it away for a fix and then realise its not the cluster when it comes back.

[EuroxS4]

I would rather buy a spare Ecu for that vehicle and swap it in.Its possible the current ecu may have been tampered with software wise.Not uncommon but I’ve heard lots of horror stories about shady shops in the UK doing similar modifications in order to sell a vehicle.


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