P0420 Fault on Ford Focus 03 1.4l

dec1982

Hi

I have the following fault on my 03 Ford Focus, P0420 Catalyst eff low bank 1. In Dec '08 I had the cat replaced by Advance Pitstop after I burnt the original out when the coil pack went :mad:. It cost 285, now the fault appears again, the cat isnt making noise or there is no smell of rotten eggs, any suggestions on what it may be?

Thanks

shamwari

It could be one of three things. Either
(a) the new CAT is faulty, particularly if Advanced fitted one of those horrid "Universal" cats

(b) The post CAT 02 sensor is faulty

(c) There's something amiss with the wiring or connections to the post CAT sensor

I've had this particular fault on a few cars where there were issues with misfires. In one case the CAT and the O2 sensor were replaced and the fault still occured :mad: (thankfully before it came to me). We never figured it out and the wiring was ok, the emissions were perfect, and a infra-red thermometer showed that CAT was giving off heat. Still P0420 was cropping up every couple of days. We advised the owner to bring the car to the main dealer because the misfire could have whacked the ECU.

Have you cleared the code to see if it stays clear? Also, have you got a scantool which can read live data from your car? If so, when you look at the output from the O2 sensors on a warm engine, sensor1 will be switching away, whilst sensor2 should be a fairly flat line. If sensor2 is following the trace of sensor 1 then I'd suspect either wiring or a knackered CAT. An emissions test will confirm it.