Circuit Description
The air conditioning (A/C) system uses an A/C refrigerant pressure sensor mounted in the high pressure side of the A/C refrigerant system to monitor A/C refrigerant pressure. The engine control module (ECM) uses this information to turn ON the engine coolant fans when the A/C refrigerant pressure is high and to keep the compressor disengaged when A/C refrigerant pressure is excessively high or low.
The air conditioning pressure (ACP) sensor operates like other 3-wire sensors. The ECM applies a 5-volt reference and a sensor ground to the sensor. Changes in the A/C refrigerant pressure will cause the ACP sensor input to the ECM to vary. The ECM monitors the ACP sensor signal circuit and can determine when the signal is out of the possible range of the sensor. When the signal is out of range for a prolonged period of time, the ECM will not allow the A/C compressor clutch to engage. This is done to protect the compressor.
Conditions for Setting the DTC
The A/C compressor relay circuit is a short to ground, or an open condition exists.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM will store conditions which were present when the DTC was set as Failure Records data only. |
| • | This information will not be stored in the Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
Inspect the harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal-to-wire connection at the ECM.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the A/C pressure display on the scan tool while moving the connectors and wiring harnesses related to the ACP sensor. A change in the A/C pressure display will indicate the location of the fault.
If DTC P1538 cannot be duplicated, reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Perform the Diagnostic System Check-Engine Controls. Is the system check complete? | -- | Go to Step 2 | |
2 |
Does the resistance measure within the specified value? | 0 ohms | Go to Step 3 | Go to Step 7 |
3 |
Does the test light illuminate? | -- | Go to Step 5 | Go to Step 4 |
4 | Repair a short to ground between the ignition switch terminal 4 and the A/C compressor relay terminal 86. Is the repair complete? | -- | Go to Step 9 | -- |
5 |
Does the test light illuminate? | -- | Go to Step 8 | Go to Step 6 |
6 | Repair a short to battery voltage between the ECM wiring connector terminal 41 and the A/C compressor relay terminal 86. Is the repair complete? | -- | Go to Step 9 | -- |
7 | Replace the A/C compressor relay. Is the replacement complete? | -- | Go to Step 9 | -- |
8 |
Is the replacement complete? | -- | Go to Step 9 | -- |
9 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 10 | Go to Step 2 |
10 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | System OK |
