Questions and Answers

Suburban DTCs P0420 & P0430 Q. I have a question about 1999 GMC Suburban. OBD-II shows codes P0420 and P0430. Only occurs when the car comes to stop at light. There are no driveability problems the previous owner must of had the same problem because the catalytic converters have been cleaned out.

This unit has 97,000 miles. it also has 4 O2 sensors. It is fuel injected automatic with A/C. I have monitored the 02 sensors and the voltage is in the normal range. There are no other faults.

Chris

A. These codes sound like catalyst efficency codes or EGR codes, both could be set because the catalytic converters are hollowed out. The O2 sensors behind the converters are looking to see how clean the exhaust is based on what the O2 sensors in front of the converters are seeing. If there is no catalyst material, there will be no change, therefore the PCM is saying the catalytic converters are bad.