Circuit Description

Heated Air/Fuel (A/F) sensors monitor exhaust gas oxygen content and deliver input signals to ECM. Heated A/F sensors are located on each exhaust manifold. Heated A/F sensor on rear (firewall side) exhaust manifold may also be referred to as bank No. 1 sensor No. 1. Heated A/F sensor on front (radiator side) exhaust manifold may also be referred to as bank No. 2 sensor No. 1. A/F sensors may also be referred to as A/F ratio sensors. ECM uses input signals to determine fuel injection system operation. DTC is set when A/F sensor output voltage does not change within 140 seconds after engine is started with engine at normal operating temperature, engine speed of 1500 RPM or more and with vehicle speed of 25-62 MPH. Possible causes are:

• A/F sensor circuit is open or shorted.
• Defective A/F sensor.
• Air induction system malfunction.
• Improper fuel pressure.
• Defective fuel injector.
• Exhaust system leak.
• Vehicle has run out of fuel.
• Defective ECM.
• Defective Positive Crankcase Ventilation (PCV) valve or hose.