Hi,

car: Ford Fiesta 2004 1.4i Zetec engine, current mileage 45,000,
fault: p0420 error code

First time poster and was wondering if any one can help. Have read through the forums and have got a lot of useful info on p0420 code which is "Catalyst System Efficiency Below Threshold (Bank 1)".

I know that this can be a number of different causes to this code. I have run an OBDii diagnostic check with a scanner hooked up to my laptop and have recorded the O2 sensor voltage output. I warmed the car up by driving it for 20 minutes and then hooked it up. From what I can tell the voltage of the front O2 sensor fluctuates between 0.1 and 0.9v and responds to throttle almost instantly. The rear 02 sensor voltage seems a lot flatter on the graph with smaller fluctuations.

I have attached two graphs one of the car idling at 750 rpm and the other of the car at 1500 going up to 2500rpm. One each picture the 02 sensor voltage is shown by the bottom graphs with the blue line being the front 02 sensor and the yellow being the rear.

On the first graph, when it is idling, the time between the front O2 sensor reading a high voltage (~0.9v) and then it dropping down and reading a high voltage again is about 3-4 secs.

If any one can tell me whether they think there is any problems with the O2 sensors I would really appreciate it. If you need any more info please ask. Thanks very much for your time.

o2 sensor at idle
www.screencast.com/users/JonScott/folders/Jing/med...8

o2 sensor at 1500-2500rpm
www.screencast.com/users/JonScott/folders/Jing/med...e

Edited by jimmyc on 06/04/2011 at 20:19