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For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Aurora 🢒 Engine 🢒 Engine Controls - 3.5L 🢒 DTC P0506

Circuit Description

The idle air control (IAC) valve is located in the throttle body of both the throttle bowl injection (TBI) and the multi-port fuel injection (MFI) systems. 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 every time the polarity of a winding is changed. This change in the 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 in order to determine the 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 commanded in order to determine the IAC pintle position. The PCM uses the IAC valve in order to control the engine idle speed 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. 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 engine coolant temperature (ECT) is more than 70°C (158°F).
    • The intake air temperature (IAT) is more than -18°C (0°F).
    • The barometric pressure (BARO) is more than 65 kPa.
    • The ignition voltage is between 9 volts and 18 volts.
    • The throttle position (TP) angle is less than 1.5 percent.
    • The vehicle speed 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 criteria must be met and fail 5 consecutive times in order to set this diagnostic trouble code (DTC).

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.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Inspect for the following conditions:

    •  A restricted air intake system
    • Proper operation and installation of all air intake components. Inspect for a collapsed, clogged, or loose air intake ducts, a clogged air filter, and proper operation of the mass air flow (MAF) 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 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 Rough, Unstable, or Incorrect Idle and Stalling .
    • If the problem is intermittent, refer to Intermittent Conditions .

Test Description

  1. This test will determine the ability of the engine controller circuit and the IAC valve circuit to control the IAC valve.

    2.

  2. 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.

DTC P0506, P1508 Idle Speed Low Table

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important:  Ensure that the engine speed stabilizes with each commanded RPM change in order to determine if the engine speed stays within 75 RPM of the commanded RPM.

  1. Set the parking brake, and block the drive wheels.
  2. Install a scan tool.
  3. Start the engine.
  4. Turn OFF all accessories.
  5. With the scan tool RPM control function slowly increment engine speed to 1,800 RPM, then to 600 RPM, then to 1,800 RPM.
  6. Exit the RPM control function.

Does the engine speed stabilize within 75 RPM of the commanded RPM during the above test?

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text or as close as possible to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the IAC valve
  3. Connect a J 37027-A IAC System Motor Analyzer to the IAC valve.
  4. Start the engine.
  5. With the IAC motor driver, command the IAC valve in until near 600 RPM is reached.
  6. With the IAC motor driver, command the IAC valve out until near 1,800 RPM is reached.
  7. Return engine speed to the desired idle, as indicated on the scan tool data list.

Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1,800 RPM when the IAC valve was commanded in and out?

Go to Step 5

Go to Step 10

5

  1. With a test lamp connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using the J 35616 connector test adapter kit.
  2. Start the engine.
  3. With the IAC motor driver, command low RPM while observing a scan tool until the IAC Counts start to increment.
  4. While the IAC Counts are incrementing, observe the test lamp.
  5. Return the engine idle speed to the desired idle, as indicated on the scan tool data list.
  6. Repeat the above procedure for the other 3 IAC valve circuits.

Did the test lamp remain ON, never flashing, while the IAC Counts were incrementing at any of the IAC valve circuits during the above test?

Go to Step 9

Go to Step 6

6

Did the test lamp remain OFF, never flashing, while the IAC Counts were incrementing at any of the IAC valve circuits during the above test?

Go to Step 8

Go to Step 7

7

  1. Connect a test lamp between the IAC coil A low circuit and the IAC coil A high circuit at the IAC valve harness connector using the J 35616 .
  2. With the IAC motor driver, command low RPM while observing a scan tool until the IAC counts start to increment.
  3. While the IAC counts are incrementing, observe the test lamp.
  4. Return the engine idle speed to the desired idle, as indicated on the scan tool data list.
  5. Repeat the above procedure with the test lamp connected between the IAC coil B low circuit and the IAC coil B high circuit at the IAC valve harness connector.
  6. Return the engine speed to the desired idle, as indicated on the scan tool data list.

Did the test lamp stay illuminated, never flashing, while the IAC counts were incrementing during the above test?

Go to Diagnostic Aids

Go to Step 14

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM harness connectors.
  3. With a DMM, test for an open or for a short to ground on the IAC valve circuit where the test lamp remained off. Refer to Circuit Testing , and refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

9
  1. Turn ON the ignition.
  2. With a DMM, test for a short to voltage on the IAC valve circuit where the test lamp remained illuminated. Refer to Circuit Testing , and refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

10

Inspect for the following conditions:

    • Throttle body damage and tampering, and throttle lever screw tampering, if the vehicle has this equipment
    • A restricted air intake system--Inspect for a possible collapsed or clogged air intake duct before and after the air filter element), for a restricted air filter element, and for a restriction at the throttle body intake screen, if the vehicle has this equipment
    • Remove the IAC valve. Refer to Idle Air Control Valve Replacement . Inspect for:
       - A clogged IAC passage
       - Excessive deposits on the throttle plate
       - Excessive deposits in the throttle bore
       - Excessive deposits on IAC Valve pintle

Repair any of the above conditions as necessary. Refer to the appropriate repair procedure.

Did you find and correct the condition?

Go to Step 15

Go to Step 12

11

Inspect for a poor connection at the PCM harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections , and refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

12

Inspect for a poor connection at the IAC valve harness connector. Refer to Testing for Intermittent Conditions and Poor Connections , and refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

13

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

Did you complete the replacement?

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC run and pass?

Go to Step 16

Go to Step 2

16

With a scan tool observe the stored information, Capture info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK