P0508-IDLE AIR CONTROL VALVE SENSE CIRCUIT LOW
For a complete wiring diagram Refer to Section 8W.
- When Monitored:
Engine running. Battery voltage greater than 10 volts. IAC motor operating.
- Set Condition:
The PCM senses a short to ground or battery voltage on any of the Linear Idle Air Control (LIAC) control circuits for 2.75 seconds while the IAC motor is active. One Trip Fault. Three good trips to turn off the MIL.
| Possible Causes |
| (K61) IAC CONTROL CIRCUIT SHORTED TO GROUND |
| (K961) IAC SIGNAL CIRCUIT OPEN |
| (K961) IAC SIGNAL CIRCUIT SHORTED TO GROUND |
| (K61) IAC CONTROL CIRCUIT OPEN |
| IAC MOTOR |
| PCM |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
Diagnostic Test
1. IAC MOTOR OPERATIONNOTE: If the engine will not idle, maintain an engine speed between 800 and 1500 RPM.
Start the engine.
Allow the engine to idle.
With a scan tool, read the IAC Current.
Is the IAC Current below 146 mA?
Yes
- Go To 2
No
- Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2. IAC MOTOR
Turn the ignition off.
Disconnect the IAC Motor harness connector.
Remove the IAC Motor.
NOTE: Inspect the IAC air passages for restrictions and damage to the IAC valve.
Measure the resistance across the IAC Motor pin terminals (component).
Is the resistance 9.7 +/- 1.0 ohms?
Yes
- Go To 3
No
- Replace the IAC Motor.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
3. (K961) IAC SIGNAL CIRCUIT OPEN
Disconnect the C2 PCM harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (K961) IAC Signal circuit from the IAC Motor harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes
- Go To 4
No
- Repair the open in the (K961) IAC Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
4. (K961) IAC SIGNAL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K961) IAC Signal circuit in the IAC Motor harness connector.
Is the resistance below 100 ohms?
Yes
- Repair the short to ground in the (K961) IAC Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go To 5
5. (K61) IAC CONTROL CIRCUIT OPEN
Measure the resistance of the (K61) IAC Control circuit from the IAC Motor harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes
- Go To 6
No
- Repair the open in the (K61) IAC Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
6. (K61) IAC CONTROL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K61) IAC Control circuit in the IAC Motor harness connector.
Is the resistance below 100 ohms?
Yes
- Repair the short to ground in the (K61) IAC Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go To 7
7. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Replace and program the Powertrain Control Module per Service Information.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)