P0537: evaporator temperature sensor voltage persistently low

P0537 is an evaporator air-temperature sensor low-voltage diagnosis in the cited body control module table. It identifies a debounced raw sensor voltage below 0.17 V, described as a continuous short-to-ground condition.

Timing separates a fault from wake-up behavior

The controller must have been awake for more than 25 seconds and the diagnostic must be enabled. The low-voltage result must occupy eight seconds within a ten-second window. A brief reading immediately after wake-up therefore is not equivalent to the complete documented fault condition.

The threshold concerns sensor voltage. It does not mean the evaporator's actual air temperature is below a stated temperature limit, and it does not establish refrigerant quantity or compressor performance.

What to retain and verify

Record the raw voltage and elapsed wake time rather than relying only on a converted temperature display. A persistent low voltage after the wake-up gate supplies different evidence from an erratic signal that repeatedly returns to normal.

The source lists Type B reporting over two trips. Verification should establish a normal sensor-circuit reading across an eligible observation window using the correct electrical procedure. The table does not isolate a wiring short from a connected-component problem or prescribe opening the refrigerant circuit. A temperature-sensor electrical code alone is insufficient reason to recharge the air-conditioning system or replace 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 64.