P0420 - Cat knackered?

wils978

Hiya lads! I keep getting a P0420 MIL popping up. I keep clearing the code but I notice it comes on when the engine is idle. So here are some diagnostics from the op-com:

Z22SE, 2.2 Astra 2003 Convertible.

Total number of fault codes: 1

OP-COM - KW2000 Communication Window> 2003 (3)|Astra-G|Engine|Z 22 SE
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
(00) - Present

See attached file.

I've removed all the unnecessary data but I can provide the whole lot if required.

If you look at columns F & G, the voltages are jumping all over the place. From what I've read, column G should be very steady. The engine was very hot & I got the readings straight after a good 15 miles journey so the cat was hot.

Suggestions? I think it's the cat because the mV are all over the place on the second sensor. I could be wrong which is why your good advice would be appreciated 🙂.

Thanks you!

Sjdickso

Have you got a standard CAT? It could just be the second sensor going lazy.

flatbeat

Could be the sensor 2 try a car cleaner first

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vx-chris

Or do what I did when I kept getting that code........unhook the battery to reset the ecu. Worked for me and I've driven over 300 miles since with no more fault. Not saying it will work but its got to be worth a try (y)

wils978

I've run cataclean twice. I've reset the ECU multiple times too. P0420 is soo common but such a grey area. The cat looks rusty as heck & many years old. It looks like it's going to be a cat off & have a good look inside job as no one knows.

IDI_AMIN

Another problem I've also had. i have changed the front o2 sensor never solved the problem with the p0420 code but did improve the mpg. Daz suggested from his experience it was the cat causing this code to come on ,so i changed the cat problem solved no more code but i never bought the type approved cat that is dearer but looks the same as the non type approved cat which is just to do with the age of your car which is from 2000 onwards. This brought me a new problem i now get the spanner light on from the first day i fitted the new cat. never had this light come on all the time i had the car. So if you need it you may be best buying the type approved cat. the part number has the letter h at the end

Matt

peng12 said:
Or do what I did when I kept getting that code........unhook the battery to reset the ecu. Worked for me and I've driven over 300 miles since with no more fault. Not saying it will work but its got to be worth a try (y)

Easier to buy a cheap fault code reader, and just keep resetting it from inside the car.

MikeS

rear lambda voltage is jumping around as if there is no cat, looks as if your cat is not doing its job correctly

i would expect your rear lambda voltage to be more static reading rich at operating temps at idle

front lambda looks fine

http://www.lambdapower.co.uk/Diagnosis/Diagnostic_index.asp#q8