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View Full Version : Please Help 2015 Audi 2.0 TDI CNHA - Black smoke



DoctorTox
22-05-2025, 07:09 PM
Good evening esteemed forum members :)

I recently acquired a bit of a problem child of a car for a proper (hopefully) steal.

It had been stage 1 tuned, DPF off and Adblue off.

When i bought it, it ran rough and low power across the whole band, with thick white smoke intermittently, and heavy black smoke on full pedal.

I was hoping it was something as simple as a bad tune, so i called in a favor and had the ECU flashed to an original file.

It runs significantly better, and the intermittent smoke is reduced, so is the black smoke, but it’s still there.

I have had it logged, and on full pedal the lambda reads a steady 0.85, which seems very low.

So heres what i know so far:

DPF is emptied out, but still in position with all the original sensors etc.
EGR is still there
Turbo was replaced by previous owner, aswell as some other things, i’m getting a list by the shop who did it.

On DTC scan i get this:

P0405 EGR valve position low input
P0403 EGR circuit malfunction
P0420 Cat converter bank 1 low efficiency
P204B Reductant pressure sensor

I have CEL and the Adblue no start in 1000km warning.

Since the DPF has been emptied i know i will need a custom map, and i fully plan on blanking the EGR and turn off Adblue aswell. But i would like to rule out any other problems before doing this to avoid issues down the line.

Any ideas?

Crasher
23-05-2025, 09:48 AM
DPF off and Adblue off.

I won't help with cars where this has been done.

DoctorTox
23-05-2025, 03:31 PM
Well, right now it’s bonestock, except for the cleared out DPF. If i could find a new DPF for a reasonable price i would have it fitted, removes any headaches about not passing MOT.

As i stated in the post, i want to fix any issues with it, and if i can have it running good without any modifications i’d be happy to.

Crasher
24-05-2025, 04:34 PM
What is the VIN?

DoctorTox
25-05-2025, 02:22 PM
Not sure why you need the VIN. A4 2015 CNHA + DSG should tell you what you need to know.

Anyways, i found some time to troubleshoot today. This is what i found:

The car has two(??) DPS’s wired in, one was kinda hidden. One had oem hose from pre-DPF + another hose which looks to be from the black inlet pipe which feeds to turbo. No idea where that hose is supposed to be originally.

The other had oem hose from post DPF + a short hose which went to atmosphere.

Both are art. No 03L 906 051 B

I ran the hoses correctly and plugged the one from inlet post MAF (does anyone know where this is supposed to go?). Both DPS’s are still wired in as i have no idea which one is the correct.

Looked at the injector data, no real irregularities there, it seems to be compensating a tiny bit for cyl 4, but not enough to worry about it.

I cleaned the MAF and MAP. Intermittent smoke is now pretty much gone, black smoke on full throttle still there although somewhat reduced.
Could it be a bad MAP in combination with clogged intake manifold? The manifold on this engine is water cooled, the fins oughta create some pressure difference post/pre cooling, especially if they’re clogged from a bad EGR?

Took the car for two drives around the block, like clockwork after 3-4 minutes or 2km, the car starts emitting white smoke, if i turn the car off and on, it stops but returns again after above mentioned time period.
I’m guessing this is the car trying to start DPF regen, as it believes it hasn’t regened for +35000 KMs. The unburnt fuel goes straight into the exhaust, and as the DPF is empty it just smokes.

Haven’t had a chance to look at the EGR/Adblue yet.

How much of a headache is it to remove the intake manifold on this car?