Circuit Description

Air/Fuel (A/F) sensor monitors exhaust gas oxygen content and delivers an input signal to ECM. ECM uses input signal to control air/fuel ratio. A/F sensor includes a heater. DTC is set when A/F sensor output does not change with engine speed at 1500 RPM or more, vehicle speed 25-62 MPH and throttle valve not fully closed for at least 2 minutes. Possible causes are:

• A/F sensor circuit is open or shorted.
• Defective A/F sensor.
• Air induction system malfunction.
• EGR system malfunction.
• Improper fuel pressure.
• Defective fuel injector.
• Exhaust system leak.
• Vehicle has run out of fuel.
• Defective ECM.