Diagnostic Aids

WARNING: This page is about a different car, the 2003 GMC Sonoma and 2003 Chevrolet S10 Pickup. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Never solder the HO2S wires.

Inspect for exhaust system leaks upstream of the suspect HO2S. The leak may be very small and typically be within 12 inches (30.5 cm) of the suspect HO2S.

A Malfunctioning HO2S Heater or Heater Circuit - With ignition on and engine off, the HO2S voltage displayed on a scan tool should gradually drop to less than 0.15 volt, indicating that the heater works properly. If not, disconnect the HO2S and connect a test light between the terminals C and D. If the test light does not light, repair the open in the HO2S ground circuit or the HO2S ignition 1 voltage circuit. If the test light lights, replace the HO2S.

The Intermittent Test - Use a scan tool in order to monitor this HO2S signal voltage. Move the related connectors and the wiring harness with a warm engine running at part throttle in Closed Loop. If the failure is induced, the HO2S signal voltage reading changes from the normal fluctuating voltage, above 600 mV and below 300 mV, to a fixed value around 450 mV. This may help to isolate the location of the malfunction.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside the insulation. Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Repair as necessary.