P0509

P0509-IDLE AIR CONTROL VALVE SENSE CIRCUIT HIGH

P0509-Idle Air Control Valve Sense Circuit High:

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
- (K961) IAC return circuit shorted to battery voltage
- (K61) IAC control circuit shorted to battery voltage
- (K61) IAC control circuit shorted to the (K961) IAC return circuit
- IAC motor
- PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. IAC MOTOR OPERATION

NOTE: 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.

Q: Is the IAC Current above 999 mA?

YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. IAC MOTOR

Turn the ignition off.
Disconnect the IAC Motor harness connector.
With the scan tool, monitor the IAC Current.
Ignition on, engine not running.

Q: Does the scan tool display IAC Current at 0 mA?

YES: Replace the IAC Motor. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 3




3. (K961) IAC SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE

Turn the ignition off.
Disconnect the C2 PCM harness connector.
Ignition on, engine not running.
Measure the voltage on the (K961) IAC Signal circuit in the IAC Motor harness connector.

Q: Is the voltage above 0.5 of a volt?

YES: Repair the short to battery voltage in the (K961) IAC Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 4




4. (K61) IAC CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE

Measure the voltage on the (K61) IAC Control circuit in the IAC Motor harness connector.

Q: Is the voltage above 0.5 of a volt?

YES: Repair the short to battery voltage in the (K61) IAC Control circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 5




5. (K61) IAC CONTROL CIRCUIT SHORTED TO THE (K961) IAC RETURN CIRCUIT

Turn the ignition off.
Measure the resistance across the (K961) IAC Signal circuit and the (K61) IAC Control circuit in the IAC Motor harness connector.

Q: Is the resistance below 5.0 ohms?

YES: Repair the short between the (K961) IAC Signal circuit and the (K61) IAC Control circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 6

6. 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.

Q: Were there any problems found?

YES: Repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test