Contour Enthusiasts Group Archives Forums General Troubleshooting Codes P0420 and P1131

I didn't get much feedback an earlier post, so I am posting again.

I have a 98 SVT that about a year ago (~65K miles) had the CEL illuminate. I had it tested at Autozone. 1 code returned and it was a P1131. A few days later, the light went off. I didn't worry about it.

8-9 months later, it came back on. I had it tested again and the same code P1131. So I replaced the bank 1 upper oxygen sensor. The light went out and stayed out for a 400+ mile trip over the span of 3 days and a days worth of errands around town at 6000 feet elevation. The next time it was used to "go to the store", the light came back on. I took it by Autozone lastnight, 2 codes this time, P1131 and P0420.

What could be causing the oxygen sensor to go out so quickly (~600 miles)?

Would the faulty oxygen sensor cause a misdiagnose by the PCM resulting in the P0420?

If I have a faulty pre-cat, what is the best way to go, get a new one or gut it and the one on bank2?

What is involved in gutting them?

Could this have something to do the MAF sensor?

The car now has 83K miles on it and I'm going to keep it when it is retired, so I do want to fix this problem long term. Any help appreciated.

Bryan

The 2 oxygen sensors "behind" the precats in the exhaust are part of the catalyst monitoring system. They detect the oxygen coming through the cats and if isn't within spec, you will get a P0420 or P0430. If you have a bad sensor in front of the cats, this could cause your mixture to go crazy and this will decrease the life of your cats.

IMHO, if you are having sensor problems in front of the cats, then you may have damaged a cat and that is why you are getting a P0420.

As far as the sensor problem, I would check the wiring to the sensor itself, then I would check all the components that make up your air/fuel ratio. Check the intake to make sure all is well (filter, MAF, TB, Manifolds). Also check the fuel system (Fuel Filter, Dirty injectors) and the ignition sytem (Plugs, wires and coil). If something is wrong with any of these components, it can screw up a sensor and thus a cat.

I just had a 0420 come up, and it turned out to be the MAF

M_Wren,
Did you end up replacing the MAF or did you just clean it?

Bryan

it was still under warranty, so i just took it in and they replaced it... i didn't try cleaning it. i guess i should have tried cleaning it first and (maybe) saved myself the $50 deductible

Interesting post. I had a P0420 pop up, and the Auto zone guy told me it was b/c it was a sea-level car (Atlanta) and I just moved to Los Alamos (8300 ft). Hmmm. Would thinner air make a P0420 come up?

MAF systems can work at any altitude, they need no compensation. They measure the mass of the air which is reduced at higher elevations.

A MAF causing a rich condition may overpower weak CAT's with unburnt fuel, or ruin them given enough time.

P1131-->Insuff. Switching Control Valve Sensor/Lean

P0420-->Catalyst Efficiency Below Threshold (Bank 1)

P0430-->Catalyst Efficiency Below Threshold (Bank 2)