HB25 - Check HO2S Switching

- Key "OFF".

- Inspect Electronic Engine Controls (EEC) wire harness for proper routing and for insulation that is burnt or chafed or intermittently shorted or open. Service as necessary.

- Disconnect Powertrain Control Module (PCM) and inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.

- Install breakout box and connect PCM to breakout box.

- Connect a Digital Volt/Ohm Meter (DVOM) to the suspect sensor test pin and SIG RTN at the breakout box.

- Test drive vehicle at 55 mph with minimum road load for five miles.

- Observe voltmeter for Heated Oxygen Sensor (HO2S) switching from 0.3 to 0.9 volt within three seconds.

- Did HO2S voltage switch?

Yes -- Unable to duplicate or identify fault at this time. Clear continuous memory. Clearing Diagnostic Trouble Codes

For further diagnosis, refer to Diagnosis by Symptom (Diagnostic Routines).

No -- Replace HO2S. Remove breakout box. Reconnect PCM. Rerun quick test. Quick Test Appendix (Detailed Testing Instructions)