For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The PCM monitors A/C refrigerant pressure and A/C evaporator temperature to determine if the A/C system has adequate refrigerant (R134a) charge. The PCM will disable the A/C clutch whenever A/C refrigerant charge drops below a predetermined value, to reduce the chance of compressor damage. The PCM will cycle the compressor more frequently if the charge is slightly low. The PCM determines A/C charge based on A/C refrigerant pressure and A/C evaporator temperature. The PCM uses these two inputs to calculate A/C refrigerant charge.

### Conditions for Setting the DTC

The PCM calculates refrigerant charge to be below a predetermined level.

### Action Taken When the DTC Sets

• | DTC P1543 will be stored in the PCM memory when the diagnostic runs and fails.

• | The Malfunction Indicator Lamp (MIL) will not illuminate.

• | A/C efficiency will decrease or A/C operation will be completely disabled.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in Failure Records.

### Conditions for Clearing the MIL/DTC

• | If no failures are reported by this or any other non-emission related diagnostic.

• | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.

• | PCM battery voltage is interrupted.

• | Using a Scan tool.

### Diagnostic Aids

An A/C evaporator temperature sensor and/or an A/C refrigerant pressure sensor that is slewed (shifted in value) could cause a DTC P1543.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Underhood temperature should be above 16°C (60°F), before proceeding.

2. The A/C performance test must be performed. A/C system hardware (A/C compressor, thermal expansion valve etc.) could cause a DTC P1543 to set.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Install the A/C manifold gauge set (Refer to Section 1B). Is the A/C refrigerant pressure (low side) greater than the specified value? | 45 psi | Go to Step 3 | Go to Section 1B1 for further A/C system diagnosis
3 |

1. Turn the Ignition ON, engine OFF.
2. Using a scan tool, monitor the A/C High Side pressure.
3. Compare the pressure reading on the scan tool to the reading indicated on the manifold gauge set.

Do the two readings agree within the specified range?

±10 psi

Go to Step 4

Go to Step 6

4 |

1. Start the engine.
2. Turn the A/C OFF for 10 seconds.
3. Turn the A/C ON and wait 10 seconds.

Does DTC P0531 set?

--

Go to DTC P0531 Air Conditioning (A/C) Refrigerant Pressure Sensor Performance

Go to Step 5

5 | Does the A/C compressor clutch engage? | -- | Go to Section 1B1 for further A/C system diagnosis | Go to Air Conditioning (A/C) Request Circuit Check for further A/C system diagnosis.
6 |

1. Turn the Ignition OFF.
2. Disconnect the A/C refrigerant pressure sensor.
3. Connect a test light to B+ and probe electrical harness connector terminal A.

Is the test light ON?

--

Go to Step 7

Go to Step 10

7 | Check the connection at the A/C refrigerant pressure sensor. Was a problem found? | -- | Go to Step 9 | Go to Step 8
8 | Replace the A/C refrigerant pressure sensor. Is the action complete? | -- | System OK | --
9 | Repair connector. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | System OK | --
10 | Repair open in the A/C refrigerant pressure sensor ground circuit.Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | System OK | --