P0506

CIRCUIT DESCRIPTION
The Idle Air Control (IAC) valve is located in the throttle body of both the Throttle Body Fuel Injection (TBI) and the Multiport Fuel Injection (MFI) Systems. It consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a two 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 B+ and an IAC valve circuit while the Powertrain Control Module (PCM) is attempting to change engine RPM. The test lamp will flash ON or OFF each time the polarity is changed. The 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 it has commanded to determine IAC pintle position. The PCM uses the IAC valve to control engine idle speed. It 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:
^ The engine RPM
^ The battery voltage
^ The air temperature
^ The Engine Coolant Temperature (ECT)
^ The Throttle Position (TP) sensor angle
^ The engine load
^ The 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 it 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 PO101, 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 Intake Air Temperature (IAT) is greater than -18°C (0.4°F).
^ The Barometric Pressure (BARO) is more than 70 kPa.
^ The ignition voltage is between 9-18 volts.
^ The Vehicle Speed Sensor (VSS) is less than 4.8 km/h (3 mph).
^ The (TP) sensor is less than 1.3 percent.
^ The above conditions are present for 10 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 times 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
^ Proper operation and installation of all air intake components-Inspect for collapsed, clogged, or loose air intake ducts, clogged air filter, proper operation of the Mass Air Flow sensor (MAF), 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 Idle Air Control (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 can not be overcome by the IAC valve-Refer to Symptoms - Computers and Control Systems. Symptom Related Diagnostic Procedures
^ If the problem is determined to be intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-4:

Steps 5-9:

Steps 10-16:

The numbers below refer the step numbers on the diagnostic table.
5. This test will determine the ability of the engine controller and 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 normally operating system, the test lamp should not flash while the IAC counts are incrementing.