Note. Heated oxygen sensor No. 1 refers to oxygen sensor closest to engine block. Heated oxygen sensor No. 2 refers to oxygen sensor farthest from engine block.
Note. For component location, see appropriate illustration in THEORY & OPERATION article.
Circuit Description
ECM compares waveform of heated oxygen sensor located in front of catalytic converter with waveform of heated oxygen sensor located behind catalytic converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are
- Defective catalytic converter.
- Heated oxygen sensor No. 2 circuit is open or shorted.
- Defective heated oxygen sensor No. 2.
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.