Strange warning light issue

[jonj]

I'll be amazed if anyone know this but here goes. A4 B8 2.0TDi

Some time ago my SPF warning light came on with the engine light and the coil light, the car immediately went into limp mode.

Took it to my normal garage guy, he said I could either replace the DPF or get it cleaned. Got it cleaned, no change. Went back to the cleaning company, they did a load of diagnostics, said the DPF was spotless and flows both sides were well within tolerance, it should be running fine. On the way home, filled up with fuel, drove out of the garage, coil light goes out, engine returns to full power. A bit later the DPF light goes out but the engine light stays on. Now, if I ever get another warning light on the dash say for low fuel or low washer fluid, the DPF light comes on and if left long enough will go back into limp mode. Topping up the fluid or fuel will bring everything back inline and working although the engine warning light always stays on.

 

Any ideas? My local garage guy doesn't know. I took it to an electrical specialist who just said the DPF needed replacing.

 

[Trevor]

Hi Jonj...welcome to the Forum

My first thoughts are that the vehicle is trying to go through a regeneration of the DPF but will only occur when the fuel level is near full tank (is the case with other makes)....worth filling right up and taking for a long run in lower gear and higher revs, at a constant 70 mph...this should initiate the regen process if it is trying to carry out one.

The washer fluid must be purely coincidental, I would imagine, but worth topping up anyway.

Let us know how you get on with it

Cheers  Trevor

[rbdazza]

i'm pretty sure that it will need to go through a successful regen to stop getting the warning light. regardless of whether you have had it cleaned. the better option over cleaning would have beena forced regen. 

the reason being that the ECU is not that smart; it will say there is a problem (give you the  DPF/glow  plug light) when it is blocking (back pressure is high) BUT it's usual regen cycle is based on miles traveled, not on how blocked the thing is. 

my advice would be to make sure you have over half a tank and give it a good 50 mile blast up the motorway in 5th. try and make sure theres some hills on the motorway so you can get the engine nice and hot