P0420

Hi All,

I have a 2002 25 1.4il that started throwing the p0420 error code about 6 months ago. The front catalyst is original and the rear was an aftermarket job with a suspiciously small looking converter box. Assuming the converter was the most likely cause, I bought a Bosal unit from GSF and fitted that only to have the light come back on three days later. As it has 101,000 miles on it, I next went for the front and rear 02 sensors only to have it come back again.

I've checked for air leaks and exhaust leaks but couldn't find anything so I bought an interface and checked the o2 readings for both sensors which were fine with the front swinging and the rear rippling with the short term fuel trim swinging around 0.

Bottom line, I can't see anything dodgy. There's no smoke from the exhaust, no detectable misfires and the front o2 sensor was free of soot and oil. Given the sensor readings are OK, is it worth me swapping the front cat or is there a chance that it may be a dodgy ECU?

Cheers,

Jools

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P0420

P0420

I have a P0420 [CAT system is operating below threshold] show up whenever I drive on the motorway, and it always seems to be M6 south!! daft I know, doesnt do it coming north, or on the M56!!

So, around january, car had a new cat pipe, it was good type approved one, I am not saying that its not at afault, just stating that it was new

I have a code reader, what can I check for to see if its the post cat sensor, the cat, or the pre cat sensor?

ta

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P0420