ISC Motor Position Sensor

IAC Valve Position Sensor:

To test the motor position sensor located in the idle air control (IAC) motor, proceed as follows


COMPONENT TEST

1. Connect a Scan Tool to the diagnostic connector and read the Idle Air Control Valve position.
2. With the engine at operating temperature, transmission in neutral (or PARK) and all accessories turned OFF, read the number of steps that the IAC motor is open.

Normal Value
2-20 steps

NOTE: A new vehicle (with approx. 300 miles or less) the IAC valve position sensor may show as many as 20 steps more than normal.

3. Turn the air conditioner ON and read the number of steps that the IAC motor is open. The number of steps should increase to compensate for the extra engine load.

Normal Value
8-50 steps

4. Turn the air conditioner OFF. The number of steps should return to the original value.
5. On vehicles with an automatic transmission, engage the brakes and place the transmission in DRIVE. Read the number of steps that the IAC motor is open. The number of steps should increase to compensate for the extra engine load.

Normal Value
3-40 steps




HARNESS TEST
1. Disconnect the ISC connector and turn the key to the ON position.

2. Using a voltmeter, measure the power supply voltage between the harness connector terminals 2 and ground and 4 and ground.

Voltage:
4.8 - 5.2 Volts.

3. Check for continuity of the ground circuit, between the harness connector terminal 3 and ground.

Continuity: Should exist.

4. Turn off the ignition and disconnect the ECM connector. Check for continuity (short) to ground between the engine control module harness connector terminal 72 or the motor position sensor harness connector terminal 3.

Continuity: Should not exist.

5. Check for continuity between the engine control module harness connector terminal 72 and the motor position sensor harness connector terminal 3.

Continuity: Should exist.

If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, clear the trouble codes and road test the vehicle to confirm that the repair has corrected the problem and the code doesn't return.


If the same trouble code reoccurs, it is possible that there is an intermittent failure of the component or the ECM. Check for looseness at all harness junctions and test for an intermittent failure.