P0506

CIRCUIT DESCRIPTION
The Idle Air Control (IAC) valve is located in the throttle body of the SFI system. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a 2 phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time the polarity of a winding is changed. This change in polarity can be seen when observing a test lamp connected between ground or battery positive voltage and an IAC valve circuit while the PCM is attempting to change engine RPM. The test lamp will flash on or off each time the polarity is changed. The Power Control Module (PCM) does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts. One count represents one change in polarity which equals one step of the stepper motor. The PCM counts the steps the PCM has commanded to determine IAC pintle position. The PCM uses the IAC valve to control engine idle speed. The IAC valve does this by changing the pintle position in the idle air passage of the throttle body. This varies the air flow around the throttle plate when the throttle is closed. To determine the desired position of the IAC pintle at idle or during deceleration, the PCM refers to the following inputs: engine RPM, battery voltage, air temperature, engine coolant temperature, throttle position sensor angle, engine load, and vehicle speed. When the ignition key is turned OFF after an ignition cycle, the PCM will first seat the IAC pintle in the air bypass bore and then retract the IAC pintle a predetermined amount of counts to allow the proper amount of air to bypass the throttle plate for engine start-up. This procedure is known as an IAC Reset.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0401, P0403, P0404, P0405, P0443, P1121, P1404, or P1441 are not set.
^ The engine run time is more than 2 minutes
^ The ECT is greater than 70°C (158°F)
^ The IAT is greater than -18°C (0.4°F)
^ The BARO greater than 70 kPa
^ The ignition voltage is between 9-18 volts
^ The TPS is less than 1.5 percent
^ The VSS is less than 4.8 km/h (3 mph)
^ The above conditions are present for 8 seconds.

CONDITIONS FOR SETTING THE DTC
^ The actual engine speed is 100 RPM less than the desired engine speed.
^ The diagnostic must fail 4 consecutive tests per key cycle.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
Inspect for the following conditions:
^ A restricted air intake system
^ Check for proper operation and installation of all air intake components. Inspect for collapsed, clogged, or loose air intake ducts, a clogged air filter, proper operation of the mass air flow sensor, if equipped, etc.
^ A tampered with or damaged throttle stop screw
^ A tampered with or damaged throttle plate, throttle shaft, or throttle linkage
^ Objects blocking the IAC passage or throttle bore
^ Excessive deposits in the IAC passage or on the IAC pintle
^ Excessive deposits in the throttle bore or on the throttle plate
^ Vacuum leaks
^ A low or unstable idle condition could be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to Symptoms - Computers and Control Systems. Symptom Related Diagnostic Procedures
^ If the problem is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-5:

Steps 6-11:

Steps 12-17:

The numbers below refer to the step numbers on the diagnostic table.
5. This test will determine the ability of the Engine Controller and the IAC valve circuits to control the IAC valve.
7. This test will determine the ability of the PCM to provide the IAC circuits with a ground. On a normal operating system, the test lamp should not flash while the IAC counts are incrementing.