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P0537 — Ac Evaporator Temperature Sensor Circuit Low

Generic OBD-II · all makesPowertrain (engine & transmission)

P0537 indicates the Powertrain Control Module (PCM) has detected a low voltage condition in the AC evaporator temperature sensor circuit. The sensor, typically a thermistor that varies resistance with temperature, is reading below the expected minimum threshold. This code can affect HVAC system operation and may cause comfort issues.

Symptoms

What causes it — most likely first

1. Faulty evaporator temperature sensor

The thermistor inside the sensor has failed, causing abnormally low resistance that the PCM interprets as a low voltage condition.

2. Wiring damage or short circuit

The sensor wiring harness has been damaged, chafed, or has a short to ground causing the voltage reading to drop below specifications.

3. Corroded or loose connector

The sensor connector pins are corroded, oxidized, or the connector is loose, creating a poor electrical connection that results in low voltage readings.

4. Short to ground in circuit

A wire in the sensor circuit has shorted to chassis ground, bypassing the sensor signal and causing the PCM to see a constant low voltage.

5. Refrigerant charge issues

Extremely low refrigerant levels or blockages can cause abnormal evaporator temperatures that may contribute to this code, though this is less common.

6. PCM malfunction

The PCM itself may have failed or have a software issue causing incorrect interpretation of the sensor signal; this is rare and typically last on the list of suspects.

How it's diagnosed

  1. Visually inspect the evaporator temperature sensor and its wiring for obvious damage, corrosion, or disconnected plugs
  2. Check the sensor connector for proper fit, clean any corrosion, and ensure good terminal contact
  3. Consult manufacturer specifications and test the sensor resistance at various temperatures using a multimeter
  4. Perform a voltage test at the sensor circuit with the key on to verify proper reference voltage from the PCM
  5. Check for shorts to ground in the wiring harness using a continuity tester or by measuring resistance
  6. If all else checks out, consider PCM issues as a last resort after eliminating all other causes

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0530 — Ac Refrigerant Pressure Sensor CircuitP0531 — Ac Refrigerant Pressure Sensor CircuitP0532 — Ac Refrigerant Pressure Sensor CircuitP0533 — Ac Refrigerant Pressure Sensor CircuitP0534 — Ac Refrigerant Charge LossP0535 — Ac Evaporator Temperature Sensor Circu

Frequently asked

Is it safe to drive with P0537?

Yes, the vehicle is generally drivable, but the AC system may not function properly, leading to discomfort, especially in hot weather. The code indicates a sensor/circuit issue rather than a critical engine safety concern.

Can I replace just the sensor, or do I need the entire HVAC assembly?

In most vehicles, the evaporator temperature sensor is a separate, replaceable component located in the HVAC housing or evaporator core area. However, some models may require partial HVAC disassembly to access it, which can increase labor time.

Why was I told I needed to replace the PCM for this code?

In some cases, a technician may suspect the PCM if all other causes are ruled out. However, P0537 is overwhelmingly caused by the sensor, its wiring, or connectors. PCM failure for this specific code is extremely rare, and replacing the computer should only be considered after thorough diagnosis of all other possibilities.

Will the AC work if I clear this code without fixing the problem?

Clearing the code may temporarily turn off the check engine light, but if the underlying fault remains, the code will likely return. The AC system may also default to a failsafe mode or not engage properly until the issue is resolved.