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 after 140 seconds from time engine is started, with engine speed at 1500 RPM or more, vehicle speed 25-62 MPH and throttle valve not fully closed. Possible causes are:

• Open or short in A/F sensor circuit.
• Faulty A/F sensor (bank No. 1 or 2, sensor No. 1).
• Faulty air induction system.
• Fuel pressure malfunction.
• Faulty fuel injector.
• Leaking exhaust system.
• Faulty ECM.