HB18 - Check HO2S Signal For Short to Power

Diagnostic Trouble Code (DTC) 173 refers to rear Heated Oxygen Sensor (HO2S). DTCs 137 and 177 refer to front HO2S.

HO2S always rich could be caused by:

- Moisture inside HO2S harness connector resulting in a short to power.

- HO2S circuit shorted to power.

- Key "OFF".

- Disconnect the suspect HO2S from vehicle harness.

- Inspect both ends of the connector for damaged or pushed out pins. moisture, corrosion, loose wires, etc. Service as necessary.

- Key "ON", engine "OFF".

- Measure voltage between HO2S circuit and PWR GND at the HO2S vehicle harness connector.

- Is voltage less than 0.5 volts?

Yes -- Go to HB2O. HB20 - Check HO2S For Short to Ignition Run Circuit

No -- Go to HB19. HB19 - Check For Short to Power