Inspect the front HO2S for any silicon contamination. This contamination will be indicated by a white powdery coating and this will result in a bad false voltage signal.

If contamination is evident on the HO2S, replace contaminated sensor with the new one and go to next step.

Is sensor contaminated?

	▶ Go to next step as below.
	▶ Replace HO2S(S1) and then go to "Verification of Vehicle Repair" procedure.

Warm up the engine to normal operating temperature.

Connect VMI to GDS and select "Oscilloscope".

Connect Channel A positive probe to Pin No.1(Signal) and Channel A negative probe to Pin No.2 (Gorund).

Fig.1) Engine Idle - Signal waveforms of front HO2S(the upper) and rear HO2S(the lower)

Fig.2) Approx. 2000rpm(Warm Up) - Signal waveforms of front HO2S(the upper) and rear HO2S(the lower)

Does the HO2S(S2) operate properly? (Check variation)

	▶ Go to "Verification of Vehicle Repair" procedure.
	▶ Go to "System Inspection" procedure.