| Table 1: | IAC Valve Terminal (Pin) Location |
Circuit Description
The DTC P0505 Idle Control System diagnostic monitors the voltage on the idle air control (IAC) coil circuits. The powertrain control module (PCM) controls the 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 the engine load. The IAC valve is a stepper motor design using four coils to control the pintle position. A DTC P0505 will set if the PCM detects an unexpected voltage on any of the coil control circuits.
Conditions for Running the DTC
The ignition is ON or the engine is running.
Conditions for Setting the DTC
| • | The IAC coil control circuit voltage is not within the expected value anytime the ignition is ON. |
| • | The above condition is present for 5 seconds. |
OR
| • | DTC P0500 is not set |
| • | The engine coolant temperature is at least 80°C (176°F) |
| • | The throttle position (TP) sensor indicates zero percent throttle opening. |
| • | The mass air flow (MAF) sensor indicates a larger than expected air flow reading during engine decel. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 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 3 consecutively passing trips without a fault present. |
| • | A history DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function. |
Diagnostic Aids
The IAC Motor Command 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 Motor Command readings.
The volume of air measured by the MAF sensor at idle, should be nearly equal to the volume of air supplied by the IAC system. A DTC P0505 can set if the MAF sensor indicates that the measured volume of air flow at idle is significantly more than the Calculated IAC Air Flow. Inspect the IAC system for the following conditions:
| • | A binding or malfunctioning IAC valve |
| • | An air leak into the idle air bypass passage |
| • | A bent or damaged throttle plate |
| • | A faulty or incorrectly calibrated mass air flow (MAF) sensor |
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 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 DTC P0505 diagnostic has passed. The 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 idle air control (IAC) system electrical circuits. Check the wiring harness 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.
Lock Tab | ||
3 | 2 | 1 |
6 | 5 | 4 |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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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.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. 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 DTC P0505 diagnostic has passed. The 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 | ||||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
2 |
Is there a Current or Pending DTC P0505 set? | -- | Go to Step 4 | Go to Step 3 | ||||||||
3 |
Is there a Current or Pending DTC P0505 set? | -- | Go to Step 5 | Go to Diagnostic Aids | ||||||||
4 |
Does the test lamp illuminate for both circuits? | -- | Go to Step 5 | Go to Step 8 | ||||||||
5 |
Are the resistances within the specified range? | 21-23 ohms at 20°C (68°F) | Go to Step 6 | Go to Step 9 | ||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | ||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||
8 | Repair the high resistance or the open in the ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- | ||||||||
9 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
10 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | |||||||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
