DTC Confirmation Test (Overall Function Check)

NOTE: Use the following test to check overall function of closed-loop fuel control. During this test, DTC may not be confirmed.

Malfunction is detected when ECM does not operate in closed loop. Possible causes are:

Front Heated Oxygen Sensor (HO2S) circuit open or shorted.
Defective front HO2S.
Defective front HO2S heater.

To check closed-loop operation, start engine and warm to normal operating temperature. Measure voltage between engine ground and ECM terminal No. 46 by backprobing. See Figure. Monitor voltmeter with engine at 2000 RPM. Voltage should be less than .21 volt at least once and more than .70 volt at least once.