Passat Problem - Possibly MAF sensor

disgruntled

I'm hoping someone here might be able to help me diagnose a problem on my 01 Passat 1.6. Basically the engine warning light came on a few weeks ago and the car went into limp mode and felt very low on power and a bit juddery at times, before you say, its not because its the hugely powerful 1.6 model.:rolleyes: I brought it into the local garage and he scanned to see what error codes were coming up and checked the emissions. I think that there were four errors, relating to both the MAF and the CAT if I remember correctly but emissions were fine. He thought it could be the MAF but wasnt certain so he reset the errors and said to come back in as soon as possible if it came back on again if it came back on again. I did another few hundred maybe a thousand miles before it came on again last night. Unfortunately the same mechanic cant look at it until later in the week as he is away at the moment so I'm hoping it might be something relatively straight forward that I could replace myself. I used to doing basic servicing on my old cars but they didnt have so many sensors and that kind of thing.

I hooked up my little crappy code reader I got in argos to see what it picked up and it found two errors:
p0172: System Too Rich (Bank 1)
P0420: Catalyst System Efficiency Below Threshold (Bank 1)

I'm thinking a dirty or faulty MAF sensor could be causing the p0172 error and consequently the error with the CAT. Does that make sense or am I way off?

I'm thinking check the spark plugs and leads. Check the air filter, clean the MAF and check for any cracks or leaks. Then reset the errors and see if that works. I'm just wondering if there is any way of testing the MAF or any way of knowing that it is definitely that which is causing the problem?

I'd really appreciate any help or advice.

Thanks,

Dave

crosstownk

If the MAF is faulty it will need to be confirmed by way of a dynamic test. Most of the time the MAF will not show up as faulty but under driving conditions the fault will be apparent.

What you describe could be a number of faults - possibly the lambda sensor but then it may be reading correctly and the mixture may indeed be too rich. Maybe the throttle angle is incorrect.

To be honest, further diagnosis is required. Use the knowledge of the stored fault codes and go from there but as yet you have nothing that points to any specific faulty component.

Oblomov

Easiest way to test a MAF sensor.. disconnect and drive it. the sudden improvement in perfromance is a clear indication it's faulty.

disgruntled

I think I might have narrowed down the possible cause of the problem a bit. I changed the air filter and plugs the other day and unsurprisingly the plugs were pretty coked up after the engine running rich. I also noticed a broken breather pipe between the air intake and the sump I think, so I repaired that also and then reset the error codes. I've done another hundred miles or so and the car is driving a lot better but the engine warning light has just come on again however with only one error this time, P0420: Catalyst System Efficiency Below Threshold (Bank 1). So I'm thinking it could be a faulty or dirty Lamda sensor and I'm wondering firstly if or how I might be able to test the sensor and secondly if there is any way of cleaning them because judging by the plugs I took out it could just be coked up. I'm just hoping that it might just be a sensor and not the Cat itself. Also I was reading on an American site something about using an additive to the petrol called BG44K? to supposedly clean out the system but I don't know if it would do anything for the sensors or the Cat, is there any point in even trying anything like that?


I'd really appreciate any help or advice, thank you

Heroditas

Have you checked the ignition coils by any chance? Silly question perhaps.