Engine management light! Help!

Hi all, so I bought my c3 in April, within 24hrs it needed a whole new exhaust system including cat. Since then everything has been fine until last week, the engine management light came on...I took my car to wilco for a diagnostics test and one code came back as ageing catalic converter...which my new one was only 2 months old so assume it was an old code...light was taken off and it came back 4 days later...another diagnostics test was done and still the same code :/ i then took the car for an emissions test and it passed, everything ok....no one seems to know why the light is on? Car is running fine and normal, anyone have any ideas or experience something similar? Thanks

Hi kellyjane88

kellyjane88 wrote:Hi all, so I bought my c3 in April, within 24hrs it needed a whole new exhaust system including cat. Since then everything has been fine until last week, the engine management light came on...I took my car to wilco for a diagnostics test and one code came back as ageing catalic converter...which my new one was only 2 months old so assume it was an old code...light was taken off and it came back 4 days later...another diagnostics test was done and still the same code :/ i then took the car for an emissions test and it passed, everything ok....no one seems to know why the light is on? Car is running fine and normal, anyone have any ideas or experience something similar? Thanks

The O2 sensors monitor the cat. The reading between the sensors are compared and a bad cat is indicated from those readings.
BUT if one of the sensors is bad, then the resulting calculation will be wrong. OR whatever damaged the cat originally was not repaired and its damaged the new cat.

You can do these fault reading diagnostics yourself cheaply, so to save trips to the garage just to get codes and then not know what the actual code was? Try a cheap ebay OBD2 reader or something similar from Amazon.co.uk. Make a note of the actual P codes and post them to your question. Hopefully someone can give you a suggestion on what to try when the codes are known.

Arfur Dent wrote:OR whatever damaged the cat originally was not repaired and its damaged the new cat.

No unheard of

https://pmmonline.co.uk/technical/how-use-4-gas-analyser-spot-potential-problems wrote: Technicians often resolve this situation by fitting a new cat.

Although that particular solution could reduce the CO to 0.2, as the new cat will be working at 100% (for a few weeks at least), enabling the vehicle to pass the emissions section of the MOT, this is only a short term fix. The reason being is that the CO and HC values will only reduce for a short period of time and experience suggests that there is a problem that needs to be corrected before the new cat becomes damaged.

The full article is here https://pmmonline.co.uk/technical/how-us ... l-problems

https://pmmonline.co.uk/technical/how-use-4-gas-analyser-spot-potential-problems wrote: THE IDEAL 4 GAS VALUES ARE:
CO <0.2%; CO2 >13.5%; O2 <0.2%; HC <15PPM; LAMBDA between 0.99 & 1.01 @ 2,500 rpm