2006 VW Passat failed NCT on emissions

Jimmyireland

Hi. My friends 2006 VW Passat failed NCT today on emissions. Readings as follows. Low idle 700 rpm CO 0.52 vol%. HC 222PM. High idle Lambda 1.02 3100 rpm. CO 0.76 vol%. HC 220ppm. Can anyone advise on what might be wrong. Had the cat converter done last year. Thanks.

Atlantic Dawn

Any warning lights on the dash?
Is it burning oil?
Any blueish smoke from the exhaust?

Jimmyireland

No. Nothing like that.

George Dalton

Looks like the cat again. What kind of replacement cat was fitted last year?

jimgoose

George Dalton wrote: »

Looks like the cat again. What kind of replacement cat was fitted last year?

Agreed. Probably one of these spurious cats fitted that just about get you through an NCT plus a few months. Lot of it about.

George Dalton

George Dalton wrote: »

Looks like the cat again.

George I disagree. Bad cat doesn't explain the lambda 1.02 which on the other hand would explain the rest of the results. I would blame O2 sensor or the load sensor. Needs proper diagnosis. HC of 222 is quite high for even a non-cat vehicle.

jimgoose

samih wrote: »

George I disagree. Bad cat doesn't explain the lambda 1.02 which on the other hand would explain the rest of the results. I would blame O2 sensor or the load sensor. Needs proper diagnosis. HC of 222 is quite high for even a non-cat vehicle.

A functioning cat uses a certain amount of oxygen. On the face of it, high CO and HC combined with a lean Lambda reading makes no sense, until you consider a failed cat. I've seen plenty of this. It is of course as you say a good idea to scan for OBD codes, if any, before doing much of anything.

jimgoose

jimgoose wrote: »

samih wrote: »

George I disagree. Bad cat doesn't explain the lambda 1.02 which on the other hand would explain the rest of the results. I would blame O2 sensor or the load sensor. Needs proper diagnosis. HC of 222 is quite high for even a non-cat vehicle.

A functioning cat uses a certain amount of oxygen. On the face of it, high CO and HC combined with a lean Lambda reading makes no sense, until you consider a failed cat. I've seen plenty of this. It is of course as you say a good idea to scan for OBD codes, if any, before doing much of anything.

A brand new quality cat may be efficient enough to mask small problems upstream. And too lean a mixture can result in high HC due to resulting sporadic misfire where a full cylinder of unburned charge is exhausted. 1.02 is quite a bit out (with the exception of an exhaust leak post cat).

jimgoose

samih wrote: »

A brand new quality cat may be efficient enough to mask small problems upstream. And too lean a mixture can result in high HC due to resulting sporadic misfire where a full cylinder of unburned charge is exhausted. 1.02 is quite a bit out (with the exception of an exhaust leak post cat).

Mmm. That makes a certain amount of sense too, but I should imagine you'd notice it misfiring in a case like that.

Waterson

Fuel trim data needed for accurate diagnosis