Mass Air Flow

[Crasher]

That means the Selective Catalytic Reduction system is not working as well as it should, the Reductant (AdBlue) is what the cat uses to reduce the temperature at which the soot particles will combust and turn into ash, it may just need a forced regeneration, it could need cleaning or the injector may be faulty which causes a buildup of urea crystals on the monolith that sets like concrete so the SCR unit has to be replaced. We use an endoscope down the injector port if we suspect a blockage.

[Taxiboy]

Better keep an eye on that but I wonder if the my failed Glowplug on first start of the day has caused it. The code never came back after I cleared it and I have engine off and restarted lots of times today and no codes. Also had a long job which meant going over country roads. For the past number of days the car has been good to drive and a fairly refined engine with good acceleration. Today it done an active DPF regen which took the usual 20 mins or thereabouts. I did notice before it a rather gruff sounding engine (similar to how the car has always been) and to be quiet and fast again during regen. Afterwards for the rest of my day the car drove great and refined and even with air con on I had to overtake a car and later a tractor and car in Sports mode was a flying machine. That’s the best the car has ever been. Can’t explain why it’s got better although I did pull out the Turbo Pressure sensor and connected it back the other day. See how it is tomorrow it’s got a mind of it’s own.

[Crasher]

The glow plugs are used in combustion strategy and not just cold starting and could cause a rise in soot emissions which could upset the DPF but not on an SCR car YET in my experience.

[Taxiboy]

Interesting crasher. Perhaps this has been my problem all along. For months now diesel knock was noticeable especially when cold but it’s only this week the first code has shown. The SCR code has not returned so far. Car due oil and filter change very shortly so will get the garage to fit the new Glowplug while it’s there or do it myself. Might get some DPF doctor sprayed into the DPF to give it a good clean although the previous model was a lot easier to get into at the pre car O2 sensor.

[Crasher]

Don't use snake oil treatments, just top quality fuel such as V Power.

[Taxiboy]

Replaced Glowplug myself at the weekend which I got from VW dealer. Also stuck V-Power in it on Sunday (half a tankful). Car has been driving well much better acceleration and quieter. However did notice today that diesel knock noise has returned but this time acceleration is still good. No codes showing though so will see how it is rest of the week.

[Crasher]

Once it has got clean V Power through the system it should improve, it takes a while for the ECU to react to the new fuel. One snake oil treatment I do use and have had some results with is Red Line 85 Plus

[Taxiboy]

Thanks I could give it a bash. Today the P20EE code has returned and the car is noisier due to that. One thing after another with this car.

[Crasher]

I have a feeling the SCR is blocked, it is becoming a big problem, if you let it go too far the urea crystals set like concrete and thats the end of the SCR unit.

[Taxiboy]

If that’s the case it would need to be professionally cleaned. I do wonder if the NOX sensor is faulty perhaps causing this issue. Know a few drivers both with Superb and Passat never had issues with SCR.