P1509
DTC P1509 IAC System High RPM
Circuit Description
The VCM controls idle speed with an Idle Air Control (IAC) valve. The VCM calculates the Desired RPM based on sensor inputs and the actual engine RPM. The VCM uses 4 circuits to control the IAC valve, allowing a precise amount of air into the intake manifold. In order to increase the idle RPM, the VCM will command the valve pintle to move away from its seat allowing more air to bypass the throttle plate. To decrease RPM the VCM 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 VCM 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 VCM.
This DTC is designed to determine if a high engine RPM is not responding to a decrease in IAC counts.
Conditions for Running the DTC
- No active TP sensor DTCs
- No active VS sensor DTCs
- No active ECT sensor DTCs
- No active MAP sensor DTCs
- The ECT is greater than 50 °C (122 °F).
- The system voltage is between 10 - 16 volts.
- The IAT is greater than -25 °C (-13 °F).
- The engine has been running for more than 30 seconds.
- The BARO is greater than 70 kPa.
- The MAF is between 17.5 - 50 g/s.
- The vehicle speed between 25 - 85 mph (40 - 136 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 present for more than 2 seconds.
Conditions for Setting the DTC
The change in MAF is greater than 3 g/s.
Action Taken When the DTC Sets
- The VCM illuminates the MIL (Malfunction Indicator Lamp) if a failure is detected during 2 consecutive key cycles.
- The VCM will set the DTC and records the operating conditions at the time the diagnostic fails. The VCM stores the failure information in the scan tools Freeze Frame and/or the Failure Records.
Conditions for Clearing the MIL/DTC
- The VCM 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 (coolant temperature has risen 22 °C (40 °F) from the startup coolant temperature and the engine coolant temperature is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.
Diagnostic Aids
This DTC may be caused 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 throttle 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.
- Inspect engine mounts-damaged mounts may cause tension on throttle Linkage.
- Fuel system too lean or too rich.
- Throttle body- inspect bore for foreign material.
- Refer to Rough, Unstable, or Incorrect Idle, 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 Intermittents and Poor Connections Diagnosis. If a repair is necessary, then refer to Wiring Repairs or Connector Repairs .
Steps 1 - 2:
Steps 3 - 4:
Steps 5 - 8:
Steps 9 - 14:
Steps 15 - 16:
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.
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.