Test Description

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2
   
   Check the heater current with the engine at operating temperature, and allow time for the heater current to stabilize. The HO2S 1 heater current is initially higher until the sensor reaches full operating temperature.
2. 4
   
   This step ensures that the ignition voltage circuit to the HO2S 1 is not open or shorted. The test lamp should be connected to a good chassis ground, in case the HO2S 1 low reference or HO2S 1 heater low control circuit is malfunctioning.
3. 6
   
   This step checks the HO2S 1 heater ground circuit. The engine must be running for the PCM to enable the heater low control driver to provide a path to ground.