P0538: evaporator sensor voltage high from an open or power short

The P0538 monitor evaluates evaporator air-temperature sensor voltage above 4.75 V. The cited BCM strategy associates this high-voltage signature with either a short to battery or an open circuit.

One signature, more than one electrical explanation

An open path and a path shorted toward power can produce the category described by this table. The code therefore does not select one cause or prove the temperature sensor itself has failed. It also does not mean evaporator air has reached an excessive temperature.

The controller must be awake for more than 25 seconds. Once enabled, the high reading must persist for eight seconds within a ten-second window. An isolated spike and a sustained high input should not be treated as equivalent evidence.

Confirm the circuit result

Preserve the raw voltage, wake-up timing and any evidence that separates an open path from a power-related fault. Follow the vehicle-specific electrical procedure to establish which explanation fits; the summary supplies no connector pinout or resistance specification.

Verification should show the raw input remaining valid over an eligible window. The table uses Type B, two-trip reporting, so one momentary normal display does not necessarily reflect a completed diagnostic recovery. Nothing in this monitor measures refrigerant charge or compressor output, and this code alone does not support refrigerant service or replacement of the compressor.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 65.