Many malfunctions in the electrical system are caused by poor harness and terminals.

Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

Thoroughly check all connectors (and connections) for looseness, bending, corrosion, contamination, deterioration, and/or damage.

Has a problem been found?

	▶ Repair as necessary and then go to "Verification of Vehicle Repair" procedure.
	▶ Go to "Signal Circuit Inspection" procedure.

Ignition "OFF".

Refer to "Shop Manual" and disconnect Upstream O2 Sensor connector.

Ignition "ON"

Measure voltage between Pin No. 3 (V_IP) terminal of Upstream O2 Sensor harness connector and chassis ground.

Measure voltage between Pin No. 2 (V_N) terminal of Upstream O2 Sensor harness connector and chassis ground.

Measure voltage between Pin No. 1 (V_G) terminal of Upstream O2 Sensor harness connector and chassis ground.

Measure voltage between Pin No. 6 (V_RC) terminal of Upstream O2 Sensor harness connector and chassis ground.

Re-connect Upstream O2 Sensor connector.

Ignition "OFF".

Connect VMI to GDS and set up an oscilloscope as follow (2-channel);

Channel A (+) : Pin No. 6 (V_RC) terminal of Upstream O2 Sensor.

Channel A (-) : Pin No. 1 (V_G) terminal of Upstream O2 Sensor.

Channel B (+) : Pin No. 3 (V_IP) terminal of Upstream O2 Sensor.

Channel B (-) : Pin No. 2 (V_N) terminal of Upstream O2 Sensor.

Ignition "ON" & Engine "ON".

Testing Condition : Engine Idle.

Is measured value within specification?

	▶ Go to "Component Inpsection" procedure.
	▶ Repair open or short in signal circuit between Upstream O2 Sensor and PCM and then go to "Verification of vehicle Repair" procedure.