Circuit Description
The powertrain control module (PCM) controls engine idle speed with the idle air control (IAC) valve. To increase idle speed, the PCM pulse width modulates the OPEN solenoid within the IAC valve. This action turns a cylinder within the IAC valve, allowing air to bypass the throttle plate. The PCM regulates (fast) idle speed via the IAC valve by increasing the opening of the air bypass port. The PCM regulates (slow) idle speed via the IAC valve by decreasing the opening of the air bypass port.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The PCM determines that the actual idle speed varies greatly from the desired idle speed.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction Indicator Lamp (MIL) the first time the diagnostic runs with the fault active. |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame Data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | The DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
With the engine idling at normal operating temperature and all accessories OF,F monitor the following parameters on the scan tool for correct operation:
| • | IAC Duty Cycle--27% to 43% |
| • | Electrical Load--No |
| • | Commanded A/C--Off |
Check for the following conditions:
| • | Air intake system for blockage |
| • | IAC passage or throttle bore for blockage, excessive deposits in the IAC passage and IAC pintle, and excessive deposits in the throttle bore and throttle blade. |
| • | Large vacuum leaks |
An intermittent malfunction may be caused by a fault in the IAC circuit sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connectors locks. |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
If the DTC P0505 does not reset, but a driveability symptom still exists, refer to Symptoms .
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
This step simulates the PWM signal supplied to the IAC Valve by the PCM by rapidly grounding and un-grounding terminal 1 of the IAC valve.
-
The most likely cause of no power is an open circuit condition between the IAC valve connector terminal 2 and the splice. A shorted or inoperative EFI Relay circuit will cause a no-start condition.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Does this DTC reset? | -- | ||
3 | Is there an idle quality concern? | -- | Go to Symptoms | Go to Diagnostic Aids |
4 |
Does the test lamp illuminate? | -- | ||
5 | Using a test lamp connected to BATTERY POSITIVE probe the IAC Valve connector terminal 3. Does the test lamp illuminate? | -- | ||
|
Caution: An electric fan under the hood can start up even when the engine is not running and can injure you. Keep hands, clothing and tools away from any underhood electric fan.
Insulate the terminal 1 jumper from contact to electrical ground. Does engine speed increase as the terminal 1 jumper is rapidly grounded ON and OFF? | -- | |||
7 |
Was a circuit repair made? | -- | ||
Is the action complete? | -- | -- | ||
9 | Repair the open IAC Valve ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
10 |
Important: The IAC Valve seals the coolant passage of the throttle body. Replace the IAC Valve. Refer to Idle Air Control Valve Replacement . Is the replacement complete? | -- | -- | |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the replacement complete? | -- | -- | |
12 |
Are any DTCs displayed on the scan tool? | -- | Go to the applicable DTC table. | System OK |
