H24 - Check HO2S Signal For Short to Power

With dual Heated Oxygen Sensor (HO2S), Diagnostic Trouble Code (DTC) 173 refers to right or rear HO2S; DTCs 137 and 177 refer to left or 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 (refer to schematic). H - Test Schematic

- Is voltage less than 0.5 volt?

Yes -- Go to H26. H26 - Check HO2S For Short to Ignition Run Circuit

No -- Go to H25. H25 - Check For Short to Power