Low refrigerant charge from a leak in the system; Faulty or out-of-range A/C refrigerant pressure sensor or its wiring and connector; Condenser airflow problem such as blocked condenser fins or a weak or failed cooling fan; Compressor clutch, relay or clutch circuit fault, or a worn compressor; Restriction in the system, such as a blocked orifice tube or expansion valve; Overcharge or moisture or air contamination in the refrigerant circuit; Control module fault or outdated calibration, where a known update exists for the model.

P1543

A/C System Performance.

GM
Powertrain
Manufacturer code
Low severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
43: FaultThe specific fault in that area

What it means

On GM vehicles, P1543 means the A/C System Performance fault: the control module judged that the air conditioning is not performing as expected. It typically compares A/C pressure sensor readings, compressor clutch operation, and sometimes evaporator or cabin temperature against what it expects for the conditions. The exact test and thresholds depend on the model and year.

Symptoms

A/C blows warm or only cool air
A/C compressor cycles on and off rapidly or does not engage
Poor cooling at idle or in slow traffic
A/C light or climate control fault message may appear
Cooling fans running constantly or at unexpected times

Possible causes

Low refrigerant charge from a leak in the systemlikely
Faulty or out-of-range A/C refrigerant pressure sensor or its wiring and connectorlikely
Condenser airflow problem such as blocked condenser fins or a weak or failed cooling fanpossible
Compressor clutch, relay or clutch circuit fault, or a worn compressorpossible
Restriction in the system, such as a blocked orifice tube or expansion valvepossible
Overcharge or moisture or air contamination in the refrigerant circuitrare
Control module fault or outdated calibration, where a known update exists for the modelrare

How to diagnose

Read all stored codes and freeze frame data, noting ambient conditions, engine speed and A/C request status, and check for related pressure sensor or clutch codes
Check the A/C works by feel and listen for the compressor clutch engaging and cycling
Visually inspect the A/C pressure sensor connector, wiring, relay and fuse for damage, corrosion or looseness
Inspect the condenser for blockage, debris or damaged fins and confirm the cooling fans operate correctly when A/C is requested
Check for signs of refrigerant leaks such as oily residue at pipe joints, the condenser and the compressor seals
Compare live A/C pressure sensor data with gauge readings from the system to confirm the sensor reads correctly
Measure system pressures with the engine at a stable speed and compare with the manufacturer's figures for the model
Check for relevant technical bulletins or calibration updates for the specific model and engine

How to fix

Find and repair the leak, then evacuate and recharge the system to the specified refrigerant quantity
Replace the A/C pressure sensor or repair its wiring and connector if faulty
Clean or replace the condenser, or repair the cooling fan or its circuit
Replace the compressor clutch, relay or compressor as the testing shows, and renew the drier or accumulator when the system has been opened
Replace the restricted orifice tube or expansion valve and flush the system as needed
Apply a manufacturer calibration update only if one is confirmed for the fault

Can I keep driving?

Low severity

The car can normally be driven as the fault affects comfort rather than safety. Book it in soon, as running with a leaking or failing system can damage the compressor, and if the compressor is noisy or the belt is affected, avoid using the A/C.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.