For 1990-2009 cars

### Circuit Description

The throttle actuator control (TAC) motor is controlled by the powertrain control module (PCM). The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the PCM commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase idle speed, the PCM commands the throttle plate open allowing more air to pass the throttle plate. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0506 Idle Speed Low

### Conditions for Running the DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0130, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0300, P0336, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P0641, P0651, P1512, P1514, P1516, P2101, P2135 are not set.

• | The engine is operating for at least 2 seconds.

• | The engine coolant temperature (ECT) is more than -40°C (-40°F).

• | The intake air temperature (IAT) is more than -40°C (-40°F).

• | The barometric pressure (BARO) is more than 65 kPa.

• | The system voltage is between 9-18 volts.

• | The vehicle speed is less than 4.8 km/h (3 mph).

• | DTC P0506 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

• | The actual idle speed is approximately 150 RPM lower than the desired idle speed.

• | The above condition is present for 15 seconds.

### 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.

### Test Description

The number below refers to the step number on the diagnostic table.

1. This test determines whether the engine can achieve the commanded RPM. If the engine does not reach the commanded RPM, the test determines whether the RPM is too high or too low.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Start the engine.
2. Command the engine speed up to 1,500 RPM, down to 500 RPM, and up to 1,500 RPM with a scan tool.
3. Exit the RPM control function.

Does the engine speed correspond, within 100 RPM, with each command?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 | Inspect for any condition that can reduce idle speed by increasing engine load. Examples include:

• | Incorrect torque converter clutch (TCC) operation

• | Accessories that require additional torque to operate

• | Restricted exhaust

• | Mechanical conditions that limit engine speed

Did you complete the action?

Go to Step 4

--

4 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 5

5 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK