Circuit Description

Oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to ECM. ECM uses input signal to determine fuel injection system operation. DTC is set when oxygen sensor No. 1 does not output a rich condition once engine is at normal operating temperature, engine speed of more than 1500 RPM and vehicle speed is 25-62 MPH for at least 2 minutes. Possible causes are:

• Oxygen sensor No. 1 circuit is open or shorted.
• Vehicle run out of fuel.
• Fuel system malfunction.
• Defective fuel injector.
• Ignition system malfunction.
• Exhaust system leak.
• Defective oxygen sensor No. 1.
• Defective ECM.