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DTC codes / GM codes / P1534

P1534 · GMA/C High Side Temperature Sensor Low Voltage

P1534 on a GM vehicle means the air conditioning (A/C) high side temperature sensor is reporting a voltage lower than the computer expects, which the control module interprets as an abnormally cold or shorted sensor signal. The computer has detected a low-voltage condition on the sensor circuit, typically below the normal operating range, and sets this code to flag a fault in the A/C high side temperature sensing circuit.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The A/C may blow warm air or fail to cool properly because the system cannot accurately monitor high side temperature.
  • The A/C compressor may be disabled or the system may default to a protection mode, preventing cooling.
  • The A/C control head may show erratic temperature readings or a flashing indicator.
  • Often no symptoms besides the warning light, especially if the sensor signal is only slightly out of range.
  • In some cases, the cooling fans may run continuously or not at all due to the missing temperature input.

Common causes, most likely first

  1. A short to ground in the high side temperature sensor signal circuit, often due to chafed or pinched wiring.
  2. A faulty high side temperature sensor that has internally shorted and is reporting low voltage.
  3. Corroded or loose electrical connectors at the sensor or the control module, causing high resistance or intermittent shorts.
  4. A defective A/C control module or climate control head that is misinterpreting the sensor signal.
  5. Moisture intrusion into the sensor connector or wiring harness, leading to a low-resistance path to ground.
  6. Aftermarket accessories or improper previous repairs that tapped into the sensor circuit and introduced a short.

How to diagnose and fix it

  1. Connect a scan tool and read the live data for the A/C high side temperature sensor to confirm the low voltage reading and check for related codes.
  2. Visually inspect the sensor and its wiring harness for obvious damage, corrosion, or loose connections, and repair as needed.
  3. Disconnect the sensor and measure the voltage on the signal circuit with the key on; if it is near zero, check for a short to ground in the harness.
  4. Measure the resistance of the sensor and compare it to the manufacturer's specification for the ambient temperature; replace the sensor if it is out of range.
  5. Check the sensor reference voltage and ground circuits at the sensor connector to ensure the control module is providing the correct signals.
  6. If the circuit and sensor test good, substitute a known-good sensor or use a scan tool to simulate the signal and see if the code clears.
  7. Clear the code and verify the repair by running the A/C system and confirming the sensor voltage returns to normal and the code does not reset.

Don't overlook the wiring harness

  • A common cause of P1534 that technicians miss is a short to ground in the sensor signal wire where it rubs against a metal bracket near the A/C compressor or condenser.
  • The code can be set by a faulty A/C control module even when the sensor and wiring test perfectly, so module diagnostics should be part of the workflow.
  • On some GM vehicles, the high side temperature sensor is part of the A/C pressure sensor assembly, and a failure of that combined unit can set this code without any obvious A/C performance issue.
  • Intermittent low voltage can be caused by water intrusion into the sensor connector after a car wash or heavy rain, so check for green corrosion inside the pins.
  • Do not replace the sensor blindly; a shorted signal wire will damage a new sensor or cause the code to return immediately after repair.

Can I keep driving with P1534?

You can usually drive the vehicle with this code, but the A/C may not function or may be disabled to protect the system. Avoid using the A/C until the fault is repaired, and do not ignore the code if you rely on air conditioning for defogging in humid or cold weather.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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