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 exhaust manifold above catalytic converters. See Fig 1. A/F sensor for cylinders No. 1 and 4 is referred to as bank No. 1 sensor No. 1. A/F sensor for cylinders No. 2 and 3 is 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 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 for at least 1.5 minutes. 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.
  Fig 1: Locating A/F Sensors & Heated Oxygen Sensors

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