| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM connectors and ground circuits are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. |
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.
Circuit Description
Heated oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to ECM. ECM uses input signal to determine fuel injection system operation. Heated oxygen sensor includes a heater. DTC is set when heated oxygen sensor No. 1 voltage remains at .4 volt or more, or .55 volt or less during idle, once engine is at normal operating temperature. Possible causes are
- Defective heated oxygen sensor No. 1.
- Fuel trim malfunction.
Diagnostic Aids
Using scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.