HB20 - Check HO2S For Short to Ignition Run Circuit

- Key "OFF".

- Heated Oxygen Sensor (HO2S) disconnected.

- Measure resistance between KEY PWR circuit and HO2S SIG circuit at the HO2S connector (refer to schematic).

- Is resistance greater than 10,000 ohms?

Yes -- For Diagnostic Trouble Code (DTC) 137, 173, 177: Go to HB21. HB21 - Attempt to Generate DTC 136, 172, or 176

For DTCs 17I, 174, 175 178: Go to HB22. HB22 - HO2S Check

No -- Replace HO2S. Drive vehicle 5 miles/55 mph. Rerun quick test. Quick Test Appendix (Detailed Testing Instructions)