Check eng light {follow up}

carringb wrote:
Three O2 sensor circuit codes is probably NOT the sensors OR the computer. This is either a damaged wiring harness, or simply a loose ground. A loose ground isn't uncommon on RVs because the coach builders often piggy back off the factory grounds instead of installing new ground lugs.

The O2 sensor heater circuit does need both a power and ground wire. It is not grounded through the exhaust. If neither shop tested both the ground and power wires at the sensors, you did not get the diagnosis you paid for. Yes, the PCM does supply and monitor power to the oxygen sensors, but before blaming the PCM, wiring at the sensors has to be checked first. After that is verified, then the power supply can be measured at the PCM to verify a bad board, but the sensor need to be checked first because the only way the board fails is if theres a short somewhere in the oxygen sensor circuit! Failing to fix the root cause, in case of a bad PCM, will only you earn you another new PCM in short order.