Overall Function Test

Start engine and allow it to reach normal operating temperature. Turn ignition off. Using 2 DVOMs, connect leads (backprobe) specified terminals at ECM harness connector in the following manner:

• DVOM No. 1; positive lead connected to terminal No. 46, negative lead connected to terminal No. 43.
• DVOM No. 2; positive lead connected to terminal No. 52, negative lead connected to terminal No. 106.

DVOM No. 1 is measuring front HO2S voltage and DVOM No. 2 is measuring rear HO2S voltage. Start engine and increase speed to 2000 RPM and hold steady. Monitor DVOMs and ensure DVOM No. 2 voltage switching frequency (between high and low voltage) is at least 50 percent slower than DVOM No. 1. If operation is not as specified, three-way catalyst is not operating properly. If voltage of DVOM No. 1 does not switch (between high and low voltage) more than 5 times within 10 seconds, diagnose fault in front HO2S circuit. See DTC P0133: FRONT HEATED OXYGEN SENSOR (HO2S) .