IG "OFF". Disconnect HO2S connector.

Check that the HO2S is securely installed.

Check the HO2S for contamination or damage, water intrusion in connector, incorrect fuel pressure, VAC leaks.

Is the sensor normal?

	▶ Go to "Check the Signal waveform of HO2S" as below.
	▶ Substitute with a known - good HO2S and check for proper operation. If the problem is corrected, go to "Verification of Vehicle Repair" procedure.

IG "OFF". Connect HO2S connector.

Connect probe to HO2S to measure signal waveform using oscilloscope function. Start engine.

After warming-up, monitor signal waveform of HO2S with GDS.

Fig.1) Normal waveforms of front HO2S(the upper) and rear HO2S(the lower) (chassis ground used)

Fig.2) Normal waveforms of front HO2S(the upper) and rear HO2S(the lower) (sensor ground used)

Is the sensor switching properly?

	▶ Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
	▶ Substitute with a known - good HO2S and check for proper operation. If the problem is corrected, go to "Verification of Vehicle Repair" procedure.