GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 XLR 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC P0531, P0532, or P0533

Circuit Description

The engine control module (ECM) monitors the high side refrigerant pressure through an air conditioning (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 the pressure is high, the ECM commands the cooling fans ON. When the pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0531 A/C Refrigerant Pressure Sensor Performance
    • DTC P0532 A/C Refrigerant Pressure Sensor Circuit Low Voltage
    • DTC P0533 A/C Refrigerant Pressure Sensor Circuit High Voltage

Conditions for Running the DTC
    • The engine is running.
    • A/C OFF when P0531 is set.

Conditions for Setting the DTC

P0531

The ECM detects the A/C pressure signal circuit is more than 4.5 volts for 4 minutes.

P0531

The ECM detects an A/C pressure of less than 0.1 volt for 1.6 seconds.

P0533

The ECM detects an A/C pressure of more than 4.9 volts for 1.6 seconds.

Action Taken When the DTC Sets
    • The ECM will not illuminate the malfunction indicator lamp (MIL).
    • The ECM stores the failure records.
    • The A/C compressor clutch is disabled.
    • SERVICE A/C SYSTEM displays on the driver information center (DIC).
    • A/C OFF displays on the HVAC control module.
    • The A/C compressor clutch will not be disabled if only DTC P0531 is set.

Conditions for Clearing the DTC
    • The ECM will not store failure records if only DTC P0531 is set.
    • The DTC will become history if the ECM no longer detects a failure.
    • The history DTC will clear after 40 fault-free ignition cycles.
    • Clear the DTC with a scan tool then cycle the ignition.

Diagnostic Aids

If the condition is not present, 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.

    2.

  2. 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.

    3.

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

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

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. With a scan tool, observe the air conditioning (A/C) High Side Pressure parameter in the Powertrain Engine Data 2 list.

Does the scan tool indicate that the A/C High Side Pressure parameter is within the specified range?

0.2-4.88 V

Go to Diagnostic Aids

Go to Step 3

3

  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 High Side Pressure parameter in the Powertrain Engine Data 2 list.

Does the scan tool indicate that the A/C High Side Pressure parameter is less than the specified value?

0.2 V

Go to Step 4

Go to Step 10

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the A/C refrigerant pressure sensor 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 High Side Pressure parameter in the Powertrain Engine Data 2 list.

Does the scan tool indicate that the A/C High Side Pressure parameter is greater than the specified value?

4.88 V

Go to Step 5

Go to Step 8

5

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

Does the voltage measure less than the specified value?

5.5 V

Go to Step 6

Go to Step 7

6

Does the voltage measure near the specified value?

5 V

Go to Step 12

Go to Step 11

7

Test the 5-volt reference circuit of the A/C refrigerant pressure sensor for short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

8

Test the 5-volt reference circuit of the A/C refrigerant pressure sensor for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 9

9

Test the signal circuit of the A/C refrigerant pressure sensor for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

10

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 16

Go to Step 13

11

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 16

Go to Step 13

12

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 16

Go to Step 14

13

Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

14

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 16

--

15

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

Did you complete the replacement?

--

Go to Step 16

--

16
  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