P0420 fault code

mark_eisner

Active Member
Jul 18, 2010
157
1
mark.theeisners.co.uk
I've been getting a recurring DTC: P0420: Catalyst System; Bank 1: Efficiency Below Threshold

No obvious symptoms but I think the economy is reduced (running rich?)

It's on a 1.2 12V 2003 Ibiza

I have replaced the pre-cat oxygen sensor but the code keeps coming back. The other things that the Ross-Tech wiki says are to check the catalyst and check the intake and exhaust systems. I'm assuming it means check for leaks. The exhaust system I can check easily but the intake system is a little more complex. Where are the places I should check and how do I check? I know there isn't a gapping hole in the throttle body so I assume it will be more subtle.

:(
 

graham@pioneer

Guest
We have had a couple of these and fixed them with a replacement air flow meter.
 

mark_eisner

Active Member
Jul 18, 2010
157
1
mark.theeisners.co.uk
I can't find any reference to the air flow meter (MAF) for the 1.2. I've looked on parts sites and in my haynes manual, the only reference is for diesels.

Is the part you mean the joint intake pressure/temperature sensor. I think also MAP?
 

mark_eisner

Active Member
Jul 18, 2010
157
1
mark.theeisners.co.uk
Not sure yet, am going for a drive in about 20 mins, the fault code usually only came on after the second motorway journey. It was fine on the first 70 then the code came back up the second time. Quite predictably actually.