For 1990-2009 cars

Table 1: | IAC Valve Terminal (Pin) Location

### Circuit Description

The DTC P0505 Idle Control System diagnostic monitors engine speed in order to determine the status of the idle air control (IAC) system. The powertrain control module (PCM) controls the idle air control (IAC) valve in order to regulate the air flow through the idle air bypass passage. The amount of air flowing through the idle air bypass passage determines the idle speed. The PCM directs the IAC valve according to changes in engine load. A stalling or poor idle concern could be caused by the IAC valve not operating properly.

### Conditions for Running the DTC

• | The barometric pressure is more than 75 kPa.

• | The intake air temperature is more than -8°C (+18°F).

• | The engine coolant temperature is more than 70°C (158°F).

• | The engine is running in closed loop.

• | The throttle is closed.

• | The A/C is OFF.

• | The P/S pressure switch is OFF.

### Conditions for Setting the DTC

The actual engine speed is 100 RPM lower than the target engine speed value for longer then 20 seconds.

OR

The actual engine speed is 200 RPM more than the target engine speed value for longer then 20 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after three consecutively passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

The IAC duty cycle parameter of the scan tool will appear fixed when a CURRENT or PENDING DTC P0505 is set. Clear the DTC in order to observe present time IAC Duty Cycle readings.

If the DTC P0505 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0505 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0505 appears in the Not Ran Since Code Cleared list, the P0505 diagnostic has not yet run. When the DTC P0505 does not appear in the Not Ran Since Code Cleared list, the P0505 diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the P0505 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the IAC system electrical circuits. Inspect the electrical wiring and components for an intermittent condition. Refer to Intermittent Conditions .

Use the following table in order to locate the correct terminals to test during diagnosis. The table layout corresponds to the pin location of the IAC valve electrical terminals.

#### IAC Valve Terminal (Pin) Location

Lock Tab
3 | 2 | 1
6 | 5 | 4

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step prompts the technician to check for any condition that can affect the ability of the IAC valve to control engine idle speed. A DTC P0505 can set even if there is no fault in the IAC system. Any condition that can affect the idle speed of the engine must be repaired first, in order to enable proper diagnosis of the DTC P0505.

3. This step tests whether the PCM can operate the IAC valve with the scan tool. The IAC valve can be commanded to increase/decrease engine speed by using the scan tool's RPM Control function. The RPM Control function of the scan tool is disabled when any DTCs are set, and when the engine is below the normal operating temperature of 80°C (176°F).

4. This step checks whether the malfunction that caused the DTC P0505 is still present. Operating the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0505 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0505 appears in the Not Ran Since Code Cleared list, the DTC P0505 diagnostic has not yet run. When the DTC P0505 does not appear in the Not Ran Since Code Cleared list, the DTC P0505 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0505 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

5. This step checks the electrical circuits between the IAC valve and the PCM.

6. This step checks whether the PCM is attempting to control the IAC valve. Each IAC coil control circuit should indicate high voltage (12 volts or more) and then low voltage (0.0-1.0 volts) as the PCM commands changes in the engine speed. Remember to clear any DTCs, and run the engine to normal operating temperature before attempting RPM control with the scan tool.

7. This step checks whether the malfunction that caused the DTC P0505 is still present. Road testing the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0505 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0505 appears in the Not Ran Since Code Cleared list, the DTC P0505 diagnostic has not yet run. When the DTC P0505 does not appear in the Not Ran Since Code Cleared list, the DTC P0505 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0505 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

Step | Action | Value(s) | 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 |

1. Inspect the engine for any of the following conditions:

• | Stuck or binding throttle valve, accelerator cable, or accelerator pedal

• | Vacuum or intake air leaks

• | Exhaust gas recirculation (EGR) or evaporative emission (EVAP) system malfunction

• | Incorrect throttle position (TP) sensor, engine coolant temperature (ECT) sensor, or mass air flow (MAF) sensor input

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 5

Go to Step 3

3 |

1. Turn ON the ignition, leaving the engine OFF.
2. Perform the scan tool Clear DTC Information function.
3. Start the engine.
4. Run the engine for 1 minute.
5. Check for DTCs.

Is there a CURRENT or PENDING DTC P0505 set?

--

Go to Step 7

Go to Step 4

4 |

1. Start the engine.
2. Operate the engine at normal operating temperature.
3. Select RPM Control, under IAC System, in the Special Functions menu of the scan tool.
4. Command the IAC valve to increase engine speed and decrease engine speed with the scan tool.

Did the engine speed increase and decrease when commanded by the scan tool?

--

Go to Step 5

Go to Step 7

5 |

1. Turn ON the ignition, leaving the engine OFF.
2. Perform the scan tool Clear DTC Information function.
3. Operate the vehicle within the Freeze Frame conditions as specified or until the DTC P0505 diagnostic test has run.

Is a DTC P0505 set?

--

Go to Step 7

Go to Step 6

6 |

1. Start the engine.
2. Turn OFF all accessories.
3. Operate the engine at normal operating temperature.
4. Observe the Engine Speed and IAC Duty Cycle parameters on the scan tool.

Are the Engine Speed and IAC Duty Cycle parameters within the specified values?

700-800 RPM in P/N

10% to 30% IAC Duty Cycle

System OK

Go to Rough, Unstable, or Incorrect Idle and Stalling

7 |

1. Turn OFF the ignition.
2. Disconnect the IAC valve electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Probe both IAC valve ignition positive voltage circuits, harness side, with a test lamp connected to ground.

Did the test lamp illuminate for both circuits?

--

Go to Step 8

Go to Step 11

8 |

1. Disconnect the IAC valve electrical connector.
2. Measure the resistance of the following IAC valve coil windings with a DMM:

• | Between pin 1 and pin 2

• | Between pin 2 and pin 3

• | Between pin 5 and pin 6

• | Between pin 4 and pin 5

3. Refer to the IAC Valve Terminal Identification table in Diagnostic Aids.

Was the resistance measured within the specified values?

35-43 ohms at 20°C (68°F)

Go to Step 9

Go to Step 14

9 |

1. Turn OFF the ignition.
2. Connect the IAC valve electrical connector.
3. Disconnect the PCM electrical connector C4.
4. Turn ON the ignition, leaving the engine OFF.
5. Measure the voltage of each IAC coil control circuits at the PCM connector C4, harness side, with a DMM connected to ground.

Was the voltage of each IAC coil control circuit more than the specified value?

12 V

Go to Step 10

Go to Step 12

10 |

1. Turn OFF the ignition.
2. Connect the PCM electrical connector C4.
3. Start the engine.
4. Run the engine until normal operating temperature is attained.
5. Backprobe each IAC coil control circuit at the PCM with a DMM to connected ground.
6. Observe the voltage display on the DMM for each IAC coil control circuit while increasing and decreasing the engine speed with the scan tool RPM Control function.

Was the voltage of each IAC coil control circuit switching from high to low while increasing and decreasing the engine speed?

--

Go to Step 13

Go to Step 15

11 | Repair the high resistance or open in the ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 16 | --
12 | Repair the short to ground, open circuit, or high resistance in any IAC coil control circuit that did not measure at least 12 volts in step 10. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 16 | --
13 |

1. Remove the IAC valve. Refer to Idle Air Control Valve Replacement .
2. Inspect the idle air bypass passage for restrictions or blockage.
3. Repair as necessary.

Was a repair necessary?

--

Go to Step 16

Go to Step 14

14 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Is the action complete? | -- | Go to Step 16 | --
15 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the replacement complete? | -- | Go to Step 16 | --
16 |

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 17

Go to Step 2

17 | 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