1, 2 and 3 Digit Codes: 66

Diagnostic Chart:

Trouble Code Number
- Scan tool 66

Fault Message
- Rear Bank O2S Shorted to Voltage

Background
- Rear bank heated oxygen sensor requires a heater circuit for proper operation.
- It is supplied with battery voltage through the MFI relay (ASD relay) to provide this circuit.
- A failure in the sensors heater circuit prevents it from providing accurate data to the PCM.
- If the PCM monitors more than 1.2 volts, the sensor has shorted to heater circuit voltage.

Range of Check
- Ignition switch: ON

Set Condition
- Heated oxygen sensor output voltage is more than 1.2 volts for 3 seconds.

Probable Cause
- Heated oxygen sensor failed
- Wiring harness and connectors failed
- PCM failed