3. Check HO2S Signal Waveform

1. Reconnect the HO2S and ECM connectors.
2. Warm up the engine to normal operating temperature.
3. Using a Hi-Scan (Pro), monitor the HO2S signal waveform.

Do the rear HO2S signals fluctuate between OV and 1V? 

Yes: Proceed with ECM problem procedure.

No: Replace HO2S.