GM Service Manual Online
For 1990-2009 cars only

Object Number: 574381  Size: SF
Engine Controls Components
MAF, IAC, and Knock Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM controls engine idle speed by adjusting the position of the idle air control (IAC) motor pintle. The IAC is a bi-directional motor driven by two coils. The PCM sends pulses (steps) to the IAC to extend or retract the IAC pintle into a passage in the throttle body to decrease or increase air flow. The commanded IAC position (displayed in counts) can be monitored on the scan tool. A lower number of counts indicates less commanded airflow (pintle extended). This method allows highly accurate control of idle speed and quick response to changes in engine load. If the PCM detects a condition where too high of an idle speed is present and the PCM is unable to adjust idle speed by decreasing the IAC counts, DTC P0507 will set indicating a problem with the idle control system.

Conditions for Running the DTC

    • None of the following DTCs are set:
       - Vehicle speed sensor (VSS)
       - Evaporative Emissions (EVAP)
       - Throttle position (TP) sensor
       - Misfire
       - Intake air temperature (IAT) sensor
       - Manifold absolute pressure (MAP) sensor
       - Fuel trim
       - Fuel injector
       - Exhaust gas recirculation (EGR) system
       - Engine coolant temperature (ECT) sensor
       - Crankshaft position (CKP) sensor
       - Mass air flow (MAF) sensor
    • The vehicle speed is less than 3 mph.
    • The engine has been running for at least 2 minutes.
    • The system voltage is between 9 and 18 volts.
    • The VIN K BARO is more than 65 kPa.
    • The VIN 1 BARO is more than 70 kPa.
    • The VIN K engine coolant temperature is more than -40°C (-40°F).
    • The VIN 1 engine coolant temperature is more than 70°C (158°F).
    • The VIN K intake air temperature is more than -40°C (-40°F).
    • The VIN 1 intake air temperature is more than -18°C (-4°F).
    • The VIN K throttle position is less than 25 percent .
    • The VIN 1 throttle position is less than 1.31 percent .

Conditions for Setting the DTC

    • VIN K--The engine speed is more than 275 RPM more than the Desired Idle (positive idle speed error more than 275 RPM).
    • VIN 1--The engine speed is more than 275 RPM more than the Desired Idle (positive idle speed error more than 275 RPM).
    • Above conditions are present for more than 15 seconds.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure.
    • The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using a scan tool.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at the PCM or IAC motor
        Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness
        Inspect the wiring harness for damage.
    • Vacuum leak
        Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, malfunctioning or incorrectly installed PCV valve, leaks at intake manifold, etc.
    • Throttle body.
        Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

DTC P0507 - Idle Air Control System RPM High

Step

Action

Values

Yes

No

1

Was the Powertrain On Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List/Type

Go to Step 3

3

  1. Start the engine.
  2. Turn OFF all accessories (A/C, rear defroster etc.).
  3. Using a scan tool, command the RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does the engine speed vary less than the specified value from each RPM command?

100 RPM

Go to Diagnostic Aids

Go to Step 4

4

  1. Disconnect the idle air control (IAC) valve.
  2. Install a J 37027-A IAC system monitor.
  3. With the engine running, command the RPM up to 1500, down to 650, and then up to 1500 while observing the node light.

Does each node light cycle red and green (never OFF)?

--

Go to Step 6

Go to Step 5

5

  1. Check the following circuits for an open, a short to voltage, or a short to ground:
  2. • The IAC A Low
    • The IAC A High
    • The IAC B Low
    • The IAC B High
  3. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems .

Was a problem found?

--

Go to Step 11

Go to Step 9

6

  1. Check for a faulty connection at the IAC harness connector.
  2. If a problem is found, replace the terminals as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems .

Was a problem found?

--

Go to Step 11

Go to Step 7

7

  1. Visually/physically inspect for the following conditions:
  2. • Any vacuum leaks
    • Any throttle body tampering (throttle lever stop screw turned)
    • A binding throttle plate or throttle shaft
    • Misadjusted or binding accelerator and cruise control cables, refer to Accelerator Control Cable Bracket Replacement .
    • A malfunctioning, missing, or incorrectly installed PCV valve, refer to Crankcase Ventilation System Inspection .
  3. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 11

Go to Step 8

8

Replace the IAC valve. Refer to Idle Air Control Valve Replacement .

Did you complete the repair?

--

Go to Step 11

--

9

  1. Check for a faulty connection at the PCM harness connector.
  2. If a problem is found, replace any terminals as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems .

Was a problem found?

--

Go to Step 11

Go to Step 10

10

Important:: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Did you complete the repair?

--

Go to Step 11

--

11

  1. Start the engine.
  2. Turn OFF all accessories (A/C, rear defroster etc.).
  3. Using a scan tool, command the RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does the engine speed vary less than the specified value from each RPM command?

100 RPM

System OK

Go to Step 2