Circuit Description
The engine control module (ECM) or powertrain control module (PCM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM/PCM commands the cooling fans ON. When pressure is too high or too low, the ECM/PCM will not allow the A/C compressor clutch to engage.
Conditions for Running the DTC
| • | Engine Running |
| • | The A/C refrigerant pressure is greater than 2,951 kPa (428 psi). |
| • | The ECM/PCM must be powered. |
Conditions for Setting the DTC
Any of the conditions for running the DTC are met for more than 500 milliseconds.
Action Taken When the DTC Sets
The ECM/PCM disables the A/C clutch.
Conditions for Clearing the DTC
| • | When the A/C refrigerant pressure drops to less than 2,068 kPa (300 psi) the ECM/PCM will clear the current DTC and go to a history DTC. If the A/C is still requested, the ECM/PCM will then enable the A/C clutch. |
| • | The DTC will become history if the ECM/PCM no longer detects a failure. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
| • | If DTC P1540 is stored as a history code it indicates that the ECM/PCM did receive a high A/C refrigerant pressure message. This code could also be caused by an intermittent short to voltage on the sensor signal circuit, which would cause the ECM/PCM to set DTC P0533. The code could be the result of an actual A/C refrigerant high-pressure condition. |
| • | It is possible for the refrigerant system pressure to exceed 2,951 kPa (428 psi) during extended engine idle speed with A/C on when engine coolant temperatures are greater than 123°C (253°F). This could be caused by: |
| - | An overcharged A/C system |
| - | A failed A/C pressure sensor |
| - | Blockage in a refrigerant line |
| - | Debris in front of the A/C condenser |
| - | Radiator or A/C condenser air shields missing or out of location |
| - | Inoperative engine cooling fans |
| - | Extended periods at idle in city traffic followed by rapid acceleration |
| - | Aftermarket products affecting cooling system performance |
| • | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
-
Tests for a short to voltage in the 5 volt reference circuit.
-
Tests for a high resistance or an open in the low reference circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Connector End View Reference: HVAC Connector End Views | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Is DTC P1540 stored as current? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
Does the scan tool indicate system pressure is within the pressure range shown on the pressure gage? | +20 to -20 psi | Go to Air Conditioning (A/C) System Performance Test in Heating, Ventilation and Air Conditioning | Go to Step 4 |
Does the scan tool indicate that the A/C pressure parameter is less than the specified value? | 0.1 V | Go to Step 5 | Go to Step 11 | |
Does the scan tool indicate that the A/C Refrigerant Pressure parameter is greater than the specified value? | 4.9 V | Go to Step 6 | Go to Step 9 | |
Does the voltage measure less than the specified value? | 4.9 V | Go to Step 7 | Go to Step 8 | |
Does the resistance measure less than the specified value? | 5 ohms | Go to Step 13 | Go to Step 12 | |
8 | Test the 5-volt reference circuit of the A/C refrigerant pressure sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 14 | |
9 | Test the 5-volt reference circuit of the A/C refrigerant pressure sensor for a short to ground, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 10 | |
10 | Test the signal circuit of the A/C refrigerant pressure sensor for a short to ground, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 14 | |
11 | Test the signal circuit of the A/C refrigerant pressure sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 14 | |
12 |
Did you find and correct the condition? | Go to Step 17 | Go to Step 14 | |
13 | Inspect for poor connections at the harness connector of the A/C refrigerant pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 15 | |
14 | Inspect for poor connections at the harness connector of the ECM or PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 16 | |
15 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | -- | Go to Step 17 | -- |
16 |
Important: Perform the programming procedure for the ECM or PCM. Replace the ECM or PCM. Refer to Engine Control Module Replacement in Engine Controls - 2.2L or Powertrain Control Module Replacement in Engine Controls - 2.0L. Did you complete the replacement? | Go to Step 17 | -- | |
17 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
