P1508

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The control module controls idle speed with an Idle Air Control (IAC) valve. The desired RPM is based on sensor inputs and the actual engine RPM. Four circuits are used in order to control the IAC valve, allowing a precise amount of air into the intake manifold. In order to increase the idle RPM, the control module will command the valve pintle to move away from its seat, allowing more air to bypass the throttle plate. To decrease RPM, the control module commands the IAC pintle to move closer to its seat, causing a lower airflow to bypass the throttle plate. A scan tool will display the control module commands to the IAC valve in counts. The higher the counts the more air is allowed to bypass the throttle plate. Lower counts indicate that less air is commanded by the control module.

This DTC is designed to detect low engine RPM that is not responding to increased IAC counts.

A low idle is 75 RPM below the desired idle.

CONDITIONS FOR RUNNING THE DTC
^ No active MAP sensor DTCs
^ No active TP sensor DTCs
^ No active VS sensor DTCs
^ No active ECT sensor DTCs
^ The ECT is more than 50°C (122°F)
^ The system voltage is between 10-16 volts.
^ The IAT is more than -25°C (-13°F).
^ The engine has been running for more than 30 seconds.
^ The BARO is more than 70 kPa.
^ The MAF is between 17.5-50 g/s.
^ The vehicle speed between 25-85 mph (40-138 km/h).
^ Any change in throttle position is less than 1 percent.
^ Any change in engine speed is less than 50 RPM.
^ The IAC valve was commanded to move a specified number of counts.
^ The above conditions are present for more than 2 seconds.

CONDITIONS FOR SETTING THE DTC
The change in MAF is more than 3 g/s.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL OR DTC
^ The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
^ Use a scan tool in order to clear the DTCs.

DIAGNOSTIC AIDS
This DTC can be set by an IAC valve which has stopped and is not responding to the VCM, a throttle stop screw that has been tampered with, or a damaged throttle or linkage. A slow, unstable, or fast idle may be caused by a non-IAC valve system problem that cannot be overcome by the IAC valve. Out of range control IAC scan tool counts will be above 60 if idle is too low and zero if idle is too high. Check for the following conditions:
^ The fuel system too lean or too rich.
^ Inspect the throttle body bore for foreign material.
^ Refer to Rough, Unstable, or Incorrect Idle and Stalling. Symptom Related Diagnostic Procedures
^ Gasket leaks
^ IAC reset is done with the scan tool.

An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.

TEST DESCRIPTION
The numbers below refer to the numbers in the diagnostic table.
5. The IAC Reset function used in this step only energizes the circuit for 2 seconds, so this function will have to be used repeatedly during this step. Also it is recommended that the J 35616-A connector test adapter kit is used during this procedure to prevent terminal damage to the IAC harness connector. This step can also be performed with the ignition ON and engine OFF.
6. If the test lamp remained ON at any of the IAC valve harness connector terminals during the IAC valve reset function the circuit is shorted to voltage. If these circuits are checked before or after the IAC valve reset function it is possible that any combination of IAC circuits could light a test lamp, this would be a normal condition.