2.0 TDI Limp Mode with P0299 + P2456 codes

[Russ_T_Nuts]

Hi, this is my first post here despite dropping in and out to view the forums over the past few years. I've been an active member of various other forums so I'm not completely new to it, but I don't post a lot and I'm new here, so hello to everyone.

I've got a 2.0 TDI Seat Alhambra (2014) which I've had for about 6 months and it's got about 65K on it. I'll try to keep this short, it frequently tries to perform a DPF regeneration and gets extremely hot, and in recent weeks it's started to go into limp mode and flashing the engine management light (glow plug light) when I give it any welly. I turn it off and back on, and it drives fine until I give it some power again at which point it goes into limp mode again and so on. I've had the DPF warning light come on a couple of times and when it does I do perform the drive in 4th gear at 60mph for 15 minutes etc as per the manual which does clear the DPF light but it still seems to be trying to do a regen all the time.

I read the car with VCDS and it said I had a P2456 error code, meaning the diesel particulate filter differential pressure sensor was sending erratic data. After reading loads of forum threads I bought the correct sensor and replaced it myself, adapting it to the car with VCDS. I was then able to drive the car fine without going into limp mode so I thought it was sorted, but yesterday it happened again. This time I've got another fault code, P0299 which relates to low boost pressure. I have noticed a couple of things:

1) When driving around town at slow-ish speeds I hear a new, low rumbly/blowing noise, like air is blowing out somewhere like maybe the wastegate is open, especially if lifting off the accelerator.

2) Whilst looking at the turbo/DPF area under the bonnet I had my wife start the engine and I saw a very small puff of smoke (greyish) appear from somewhere around the turbocharger. I asked her to turn off the engine and restart it, and again there was the puff of smoke. It happens immediately when the engine starts, and smells of exhaust fumes so I guess that's exactly what it is. I've noticed a new smell of exhaust in the car when stopping at lights etc, so I'm thinking I've possibly got an exhaust leak.

Would an exhaust leak somewhere in the region of the turbo/DPF possibly cause a low boost situation? I've got all sorts of thoughts in my head about the EGR and the diverter valve or a blocked DPF but I'm hoping somebody who knows about these things might be able to shed some light on it. Any ideas, please?


Many thanks!

[Belle427]

My thinking would be a restricted exhaust flow especially as your getting dpf related codes.
Just a guess.

[Patch1875]

My friend has an 2.0tdi Audi had a similar fault which pointed at a pressure sensor but turned out the EGR cooler pipe was coked up.

[Russ_T_Nuts]

Belle427 said:

My thinking would be a restricted exhaust flow especially as your getting dpf related codes.
Just a guess.

Yes, I'm thinking something like that. Many thanks.

[Russ_T_Nuts]

Patch1875 said:

My friend has an 2.0tdi Audi had a similar fault which pointed at a pressure sensor but turned out the EGR cooler pipe was coked up.

Thanks for that info. The EGR valve is one of the various possible causes that I've added to the list. When you mention EGR cooler pipe, do you mean one of the metal pipes that carries exhaust gases to/from the EGR valve, or do you mean one of the water pipes that are connected to it (or something else)?

Cheers

[Russ_T_Nuts]

If it makes any difference at all, I've taken some details from VCDS and will list them below. The engine was not running at the time therefore I don't know which of these are relevant:

Particle filter: difference pressure -10 hPa
Particle filter: offset for differential press. 0 hPa
Particle filter: time since last generation 3283 s
Particle filter: oil ash volume 0.07 l
Particle filter: soot mass calculated 13.14 g
Particle filter: soot mass measured 22.88 g
Particle filter: kilometers since last regeneration 8969 m (8.97km)
Particle filter differential press. sensor: uncond. voltage 1001.8 mV
Simulated particle filter surface temperature 67.9 degrees C

I've got a feeling the DPF is partially blocked/melted so exhaust is forcing its self out somewhere else hence the puff of exhaust I see from the turbo area (not from the exhaust at the back of the car) when the engine starts. I still haven't been able to ascertain exactly where it's coming from. Also, I tried to perform a service regeneration (standing) via VCDS and it aborted immediately for safety reasons, but the ash levels don't look all that high?

Edited by Russ_T_Nuts on Tuesday 9th March 13:21

[Belle427]

May be well worth seeking out a recommended specialist in diesels and dpf related issues, they will have probably seen these faults before.
It’s very hard to guess at this stuff.

[Russ_T_Nuts]

Belle427 said:

May be well worth seeking out a recommended specialist in diesels and dpf related issues, they will have probably seen these faults before.
It’s very hard to guess at this stuff.

Yes you're right, and It's looking that way unfortunately. Luckily there's a reputable VAG specialist right around the corner from me. When I do go to a garage for work, I usually like to go armed with a good idea of what's gone wrong and what needs doing to fix it. This afternoon I used an allen key to tighten up the clamp that holds the turbo's exhaust outlet to the inlet on the DPF. I was able to give it a full turn quite easily so maybe that'll help. I've not had much chance to test it yet, we'll see how it goes.

Thanks

[Patch1875]

Russ_T_Nuts said:

Thanks for that info. The EGR valve is one of the various possible causes that I've added to the list. When you mention EGR cooler pipe, do you mean one of the metal pipes that carries exhaust gases to/from the EGR valve, or do you mean one of the water pipes that are connected to it (or something else)?

Cheers

It must be an exhaust pipe as it’s soot that builds up in the pipe the mechanic fixing said it’s a common issue and is only identified by taking the pipe off to check didn’t have any fault codes that pointed specifically to that.

[Russ_T_Nuts]

Update - I've found there's black soot on and around the turbo. It's not oil, it's very dry, black, powdery soot. Initially I found it around the clamp that holds the DPF onto the exhaust side of the turbocharger body, so I think exhaust is leaking from there, but I subsequently found another load of it on the turbo when I put my hand down between the back of the engine and the bulkhead to feel the area of the actuator rod etc. The exhaust smell under the bonnet and the puff of smoke I see from that area when the engine starts would both seem to suggest an exhaust leak of some kind, I believe. Is that something which is common to these engines/turbos? It would be handy to know where to start looking for a leak. Turbo? Turbo to DPF clamp? Something below the turbo maybe (cracked metal EGR pipe)? Something else maybe that goes on these?

Thanks!

[crashS2K]

Hi,

I’ve recently had similar problems with my 2011 Seat Alhambra 2.0 TDI. Not had many long journeys since last August when we took it to France. Did a DPF regen due to glow plug light going on as per handbook (driving 45mph in 4th gear for 15mins+).

Recent trip joining M1 and glow plug goes on and engine goes into limp mode. Scanned fault code of P029900 turbo underboost.

Tried a static regen via VCDS but problem persists. Also fans continuing to run after engine is turned off which suggests car is attempting to do a DPF regen.

Took it to local indie who suspect that the main (secondary?) cat is blocked / damaged due to excessive adblue injection post emissions ‘fix’ that VW rolled out a few years ago and that it needs to be replaced at a cost of over £2k which isn’t really economically viable.

Hope that helps - how are you getting on with yours?

[Russ_T_Nuts]

Thanks for replying. Mine's in the garage now, I'll update again when I know more. I've been beginning to suspect it's a cat issue so what you said about yours makes sense.

Cheers!

[Russ_T_Nuts]

Russ_T_Nuts said:

Thanks for replying. Mine's in the garage now, I'll update again when I know more. I've been beginning to suspect it's a cat issue so what you said about yours makes sense.

Cheers!

Well it's still in the garage now, and we're still none the wiser as to what it might be. I have tried to say that it could well be the cat blocked due to the reductant injector but I'm not sure they took that onboard to be honest, as it could be caused by any one of dozens of things on a list as long as your arm.

[ODB1001]

Hi, I have this exact same issue. Did you ever find out what the cause was?

[Russ_T_Nuts]

ODB1001 said:

Hi, I have this exact same issue. Did you ever find out what the cause was?

Hi, sorry to hear you're having the same problem. The local specialist said a new turbo was required, I doubted that but I'm no expert and had no other choice so I had them fit a new turbo and, to my surprise, that did actually seem to fix the issues we were having. Fingers crossed it's been ok since. We think the problem was caused by the DPF getting so clogged that it wouldn't run its regeneration cycle (the garage eventually forced this to happen, I wasn't able to do it myself) and that in the long run caused some kind of turbo damage. I made sure I kept the old turbo for inspection and to be honest it looks absolutely fine to me, no melting or missing bits from the turbine or compressor, no play in the bearing, but could be the variable nozzles etc. I don't know. But ultimately we had to throw money at it to fix it. Make sure you keep the AdBlu topped up and the diesel above 1/4 full or the DPF will not regenerate when it needs to. I hope that helps at least a bit.