PO420 code

[EMT96]

Anyone ever have the PO420 code on their 1996 chevy truck ? If so how did you fix it ?

 

[Mike]

Means you need new cats and probably o2 sensors.

 

[1990GMCSIERRA]

could just be the sensors gone bad

 

[daddy_dandy]

Have you noticed a significant drop in performance/mileage? IF so, check your fuel pressure to make sure it's within spec. If you're running overly rich for an extended period of time, it will destroy your catalytic converters. So, make sure the fuel system is healthy before you replace them otherwise you'll be doing it again in short order. Also, hook a scanner up and look at your ECT temps to make sure your ECT sensor is functioning properly. If that sensor is bad, it will dump fuel, again destroying your catalytic converters.

Magnaflow converters are a nice replacement, especially if you still have the stock exhaust system. If you're not stock, consider the high flow ones. They work well to.

If you're replacing the O2 sensors, DO NOT BUY BOSCH OXYGEN SENSORS!!!!! Go Delphi/Delco. Rockauto.com usually has the best prices. DO NOT BUY BOSCH OXYGEN SENSORS!!!!!

 

[daddy_dandy]

Hook up a scanner to check your oxygen sensors for proper operation. You should see them "refreshing" or "switching" about every 1-2 seconds. Any more than that, like 3-5 seconds and they're bad. Buy a scanner if you don't have one. It's the greatest tool you can own.

 

[EMT96]

Thanks for the input fellas. The cat was bad and the sensors are still good.

 

[1990GMCSIERRA]

sweet, glad u got er fixed