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 does not output a rich condition once engine is at normal operating temperature, engine speed is more than 1500 RPM and vehicle speed is 25-62 MPH for at least 2 minutes. Possible causes are:

• Heated oxygen sensor No. 1 circuit is open or shorted.
• Defective heated oxygen sensor No. 1.
• Air induction system malfunction.
• EGR system malfunction.
• Improper fuel pressure.
• Defective fuel injector.
• Exhaust system leak.
• Vehicle has run out of fuel.
• Defective ECM.