P1508

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart:

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 AC 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 indicates less air is commanded by the control module.

This Diagnostic Trouble Code (DTC) is designed to detect low engine RPM that is not responding to increased IAC counts.

CONDITIONS FOR RUNNING THE DTC
^ No active Manifold Absolute Pressure (MAP) sensor DTCs
^ No active Throttle Position (TP) sensor DTCs
^ No active Vehicle Speed Sensor (VSS) DTCs
^ No active Engine Coolant Temperature (ECT) sensor DTCs
^ The ECT is more than 50°C (122°F).
^ The system voltage is between 10 and 16 volts.
^ The Intake Air Temperature (IAT) is more than -25°C (-13°F).
^ The engine has been running for more than 30 seconds.
^ The barometric pressure (BARO) is more than 70 kPa.
^ The Mass Air Flow (MAF) is between 17.5 and 50 g/s.
^ The vehicle speed between 25 and 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 tools Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL/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.
^ A scan tool can clear the DTCs.

DIAGNOSTIC AIDS
An IAC valve that is stopped and cannot respond to the VCM, a throttle stop screw that has been tampered with, or a damaged throttle or linkage could cause this DTC. 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:
^ Fuel system is too lean and rich.
^ Throttle body - Inspect the bore for foreign material.
^ Refer to Rough, Unstable, or Incorrect Idle and Stalling. Rough, Unstable, or Incorrect Idle and Stalling
^ 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 check 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 step numbers on 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.