GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2006 🢒 ION 🢒 Restraints 🢒 SIR 🢒 DTC P1540

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.

DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC P1540 Air Conditioning (A/C) Refrigerant Overpressure - Air Conditioning (A/C) Disabled

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 .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Tests for the proper operation of the circuit in the low voltage range.

  1. 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.

    2.

  2. Tests for a short to voltage in the 5-volt reference circuit.

    3.

  3. 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

Schematic Reference: HVAC Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition with the engine OFF.
  3. Wait for one minute for A/C system pressure to equalize.
  4. With the scan tool , test for current and history DTCs in the engine control module (ECM) or powertrain control module (PCM) data list.

Is DTC P1540 stored as current?

--

Go to Step 3

Go to Diagnostic Aids

3
  1. Connect the J 43600 ACR 2000 Air Conditioning Service Tool. Refer to Special Tools .
  2. Observe the A/C Refrigerant Pressure parameter in the ECM or PCM Inputs/Outputs psi data list using the scan tool.

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

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the A/C refrigerant pressure sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the A/C Refrigerant Pressure parameter in the ECM or PCM, General Info Inputs/Outputs data list.

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

5

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the A/C refrigerant pressure sensor and the signal circuit of the A/C refrigerant pressure sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the A/C Refrigerant Pressure parameter in the ECM or PCM, General Info Inputs/Outputs data list.

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

6

  1. Disconnect the fused jumper wire.
  2. Measure the voltage between the 5-volt reference circuit of the A/C refrigerant pressure sensor and the low reference circuit of the A/C refrigerant pressure sensor.

Does the voltage measure less than the specified value?

4.9 V

Go to Step 7

Go to Step 8

7

  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable.
  3. Measure the resistance from the low reference circuit of the A/C refrigerant pressure sensor to a good ground.

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 .

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 .

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 .

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 .

Did you find and correct the condition?

 

Go to Step 17

Go to Step 14

12
  1. Disconnect the ECM or PCM.
  2. Test the low reference circuit of the A/C refrigerant pressure sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs .

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 .

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 .

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 .

Did you complete the replacement?

--

Go to Step 17

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16

Replace the PCM or ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

 

Go to Step 17

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17
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK