Chart A-2 Dwell Fixed Between 15 and 50 Degrees

Chart A-2:

Chart A-2 Wiring Diagram:

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Running engine at part throttle, for one minute, warms up the oxygen sensor. Grounding 02 sensor input checks ECM response to a "lean" signal. Normal response: dwell decreases to full rich command.

2. This step grounds 02 sensor circuit at the ECM to check for an open in the wiring to ECM Terminal "3." Normal response is to "lean" the signal. Dwell decreases (rich command).

3. This step checks for voltage to the coolant sensor. Normal reading on a warm engine is less than 2.5 volts. An open circuit would cause a reading of approximately 5.0 volts.

4. On some ECMs, an open in circuit to terminal "20" can cause "OPEN LOOP."

5. Checks output of 02 sensor with full rich command from ECM caused by grounding the 02 sensor input circuit. Normal response; voltage at 02 sensor should be over 0.8 volts.