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P1543

A/C System Performance.

  • Cadillac
  • 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

P1543 on a Cadillac means the A/C System Performance fault has been set. The engine control module judged that the air conditioning system is not performing as expected, usually from the A/C pressure sensor signal and the compressor clutch behaviour not matching what was commanded. The exact test and thresholds depend on the model and year.

Symptoms

  • A/C blows warm or only slightly cool air
  • A/C compressor does not engage or cycles on and off rapidly
  • A/C warning or service message, or the A/C light flashing on some models
  • Poor cooling at idle or in slow traffic
  • Engine idle change or cooling fans running unusually when A/C is selected

Possible causes

  • Low refrigerant charge due to a leak in the systemlikely
  • Faulty A/C refrigerant pressure sensor or its signal being out of rangelikely
  • Damaged wiring or poor connections at the pressure sensor, compressor clutch or relaypossible
  • Failed compressor clutch, clutch coil or A/C relaypossible
  • Restricted system, for example a blocked orifice tube or expansion valve, or a faulty condenser fan reducing heat rejectionpossible
  • Internal compressor wear or failurerare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, noting engine temperature, A/C request status and any other A/C or cooling fan codes
  2. Visually inspect the A/C pipes, condenser and compressor for oil staining, damage or debris blocking airflow
  3. Inspect the wiring and connectors at the A/C pressure sensor, compressor clutch and relay for corrosion, damage or looseness
  4. Check the A/C pressure sensor reading on a scan tool with the engine off and then running, and compare it with the actual system pressure from a gauge set
  5. Check that the compressor clutch is commanded and engages, and measure the supply voltage and ground at the clutch
  6. Check the condenser and cooling fans operate correctly when A/C is requested
  7. Test the system for leaks and check the refrigerant charge using the recovery and recharge equipment, following the specified charge for the model
  8. Check for a restriction by comparing high and low side pressures against the manufacturer's specification for the ambient temperature

How to fix

  • Find and repair the leak, then evacuate and recharge the system to the specified charge
  • Replace the A/C pressure sensor if its signal does not match actual pressure
  • Repair damaged wiring or connectors, or replace a faulty relay
  • Replace the compressor clutch or compressor if it is faulty, and replace any parts contaminated by debris
  • Clear any restriction by replacing the blocked component and the receiver or accumulator as specified for the model
  • Repair or replace faulty cooling fans or clean a blocked condenser

Can I keep driving?

Low severity

The car is generally safe to drive, as this is a comfort system fault rather than a safety one. Book it in soon, as running with low refrigerant can damage the compressor.

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

This code for other makes

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