P0508

P0508-IDLE AIR CONTROL VALVE SENSE CIRCUIT LOW







- 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.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. IAC MOTOR OPERATION

NOTE: If the engine will not idle, maintain an engine speed between 800 and 1500 RPM.

1. Start the engine.
2. Allow the engine to idle.
3. 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. Intermittent Condition Test
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. IAC MOTOR
1. Turn the ignition off.
2. Disconnect the IAC Motor harness connector.
3. Remove the IAC Motor.

NOTE: Inspect the IAC air passages for restrictions and damage to the IAC valve.

4. 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. Powertrain Verification Test

3. (K961) IAC RETURN CIRCUIT OPEN




1. 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 PCM Pinout Box 8815 to perform diagnosis.

2. Measure the resistance of the (K961) IAC Return 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 Return circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. (K961) IAC RETURN CIRCUIT SHORTED TO GROUND




1. Measure the resistance between ground and the (K961) IAC Return circuit in the IAC Motor harness connector.

Is the resistance below 100 ohms?

Yes

- Repair the short to ground in the (K961) IAC Return circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 5

5. (K61) IAC MOTOR CONTROL CIRCUIT OPEN




1. 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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

6. (K61) IAC MOTOR CONTROL CIRCUIT SHORTED TO GROUND




1. 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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 7

7. EXCESSIVE RESISTANCE IN THE (K961) IAC SIGNAL CIRCUIT

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 PCM Pinout Box 8815 along with the Adapter 8815-1 to perform the diagnosis.

1. Using a voltmeter perform a voltage drop test. Backprobe the (K961) IAC Signal circuit at the IAC harness connector and probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

2. Start the engine and allow it to reach normal operating temperature.
3. Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes

- Go To 8

No

- Repair the excessive resistance in the (K961) IAC Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

8. EXCESSIVE RESISTANCE IN THE (K61) IAC CONTROL CIRCUIT
1. Turn the ignition off.
2. Move the voltmeter leads to backprobe the (K61) IAC Control circuit at the IAC harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes

- Go To 9

No

- Repair the excessive resistance in the (K61) IAC Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

9. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

1. 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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Replace and program the Powertrain Control Module.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test