Schematic Reference: Engine Controls Schematics
Circuit Description
The Powertrain Control Module (PCM) controls engine idle speed with the Idle Air Control (IAC) valve. To increase idle speed, the PCM grounds the OPEN solenoid within the IAC valve. This action opens a plate 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. To decrease idle speed, the PCM grounds the CLOSE solenoid within the IAC valve, thus allowing less air to bypass the throttle plate. The PCM regulates (slow) idle speed via the IAC valve by decreasing the opening of the air bypass port.
When the A/C switch is turned "ON," the A/C amplifier sends the PCM an A/C "ON" signal. In return the PCM will compensate for the extra engine load via the IAC valve, and increase the idle speed. The PCM sends the A/C amplifier an A/C cut-out signal during certain heavy engine loads conditions. When the A/C amplifier receives this signal from the PCM, it will immediately cuts out the A/C compressor operation. When the engine returns to a lighter load the PCM negates the A/C cutout signal. At this point, the A/C amplifier can resume normal cycling of the A/C compressor clutch.
Conditions for Setting the DTC
Idle speed continues to vary greatly from the target speed.
Action Taken When the DTC Sets
| • | The PCM will illuminate the MIL during the second key cycle in which the DTC sets. |
| • | The PCM will store the conditions which were present when the DTC set as Freeze Frame Data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool "Clear Information" function or by disconnecting the PCM battery feed. |
Diagnostic Aids
An intermittent malfunction may be cause by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect harness connectors for backed out terminals, improper matting, broken locks, terminal-to wire connection before component replacement.
With the engine idling, normal operating temperature and all accessories "OFF" monitor the following on the scan tool for correct operation:
| • | IAC Duty Cycle - 27-43% |
| • | Electrical Load - No |
| • | Commanded A/C - Off |
| • | Idle Switch - ON |
| If any of the above are not functioning properly refer to the applicable circuit. |
Check 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. |
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 and a driveability symptom still exists, refer to Electrical Load Idle-Up Signal Circuit Check.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
-
The OBD System Check 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.
-
This step checks whether DTC P0505 is the result of a hard failure or an intermittent condition.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the "Powertrain On Board Diagnostic (OBD) System Check performed? | -- | |||
Does the scan tool parameter read within specified range? | 27-43% | |||
3 |
Does DTC P0500 set? | -- | Go to Diagnostic Aids | |
4 |
Does test light illuminate? | -- | ||
5 |
Does DMM read within the specified range? | 10-12 V | ||
6 |
Does DMM read within the specified range? | 10-12 V | ||
7 |
Does the DMM read the specified value? | 0.5 V | ||
8 |
Does the DMM read the specified value. | 12 V | ||
9 |
Does IAC valve close? | -- | ||
10 |
Does the IAC valve open? | -- | ||
11 | Repair open or short in the power feed circuit between the IAC valve connector and EFI F-HTR. Is the action complete. | -- | -- | |
12 |
Was a repair necessary? | -- | ||
13 |
Was a repair necessary? | -- | ||
14 |
Does DMM read within specified value? | 10 V | ||
15 |
Does test light illuminate? | -- | ||
16 |
Was a repair necessary? | -- | ||
17 |
Does DMM read within the specified range? | 10-12 V | ||
18 |
Does DMM read within specified voltage? | 10 V | Go to Diagnostic Aids | |
19 |
Was a repair necessary? | -- | ||
20 |
Does DMM read more than specified value? | 10 V | ||
21 |
Was a repair necessary? | -- | ||
22 | Replace the IAC valve. Is the action complete? | -- | -- | |
23 | Replace the A/C amplifier. Is the action complete? | -- | -- | |
24 | Replace the PCM. Is the action complete? | -- | -- | |
25 | After repairs, use the scan tool clear information function and road test vehicle within "Freeze Frame" conditions that set the DTC. Check for DTC(s). Review scan tool data and if no DTC(s) are stored repair is complete. Are any DTC(s) displayed on scan tool? | -- | Go to the applicable DTC table | System OK |
