P0506

CIRCUIT DESCRIPTION
The Idle Air Control (IAC) valve is located in the throttle body of both the TBI and the MFI Systems. It consists of a movable pintle, driven by a gear that is 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 B+ 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 PCM does not use a physical sensor in order to determine the IAC pintle position, but uses a predicted number of counts. One count represents one change in the polarity, which equals one step of the stepper motor. The PCM counts the steps it has commanded in order to determine the IAC pintle position. The PCM uses the IAC valve in order to control the engine idle speed. The PCM does this by changing the pintle position In the idle air passage of the throttle body. This procedure varies the air flow around the throttle plate when the throttle is closed. In order 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
^ The throttle position 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 the pintle a predetermined amount of counts in order 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, P0123, P0125, P0171, P0172, P0201- P0206, P0300, P0335, P0385, P0401, P0403, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, P1336, P1372, P1380, P1381, P1404, or P1441 are not set.
^ The engine run time is more than 2 minutes.
^ The ECT is more than 70°C (158°F).
^ The IAT is more than -18°C (0.4°F).
^ The BARO is more than 65 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 10 seconds.

CONDITIONS FOR SETTING THE DTC
^ The actual engine speed is 75 RPM less than the desired engine speed.
^ The above enabling criteria must be met and must fail 5 consecutive times in order to set this DTC.

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 tool Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL OR 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.
^ Use a scan tool in order to clear the DTCs.

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, a clogged air filter, and proper operation of the mass air flow sensor, if the vehicle has this equipment.
^ 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 the 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 can be caused by a non-IAC system condition that cannot be overcome by the IAC valve. Refer to Rough, Unstable, or Incorrect Idle and Stalling. Rough, Unstable, or Incorrect Idle and Stalling
^ If the condition is determined to be intermittent, refer to Rough, Unstable, or Incorrect Idle and Stalling. Rough, Unstable, or Incorrect Idle and Stalling

TEST DESCRIPTION

Steps 1-4:

Steps 5-9:

Steps 10-16:

The numbers below refer to 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 AC circuits with a ground. On a normally-operating system, the test lamp should not flash while the IAC counts are incrementing.