What it means
The evaporator temperature sensor signal voltage is below the lower diagnostic threshold. Indicates a short to ground or sensor fault.
How it works
The A/C evaporator temperature sensor monitors the evaporator core so the control system can prevent icing. P0537 sets when the sensor signal voltage falls below its lower diagnostic threshold, commonly because the sensor or signal circuit is shorted to ground.
Common causes
Most likely first.
- Sensor internally shorted
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
Symptoms
- A/C warning light may turn on
- Air conditioning may cool poorly or not at all
- Evaporator may freeze or airflow may decrease
How to diagnose it
- Check live A/C data to confirm the evaporator temperature signal is being reported unusually low, and review freeze-frame conditions when the fault set.
- Inspect the sensor connector and wiring for corrosion, damaged insulation, or a signal wire contacting ground.
- Check the sensor reference and ground, then measure the signal circuit against the manufacturer's specification.
- Disconnect and test the sensor and harness separately using the manufacturer's procedure to determine whether the low signal comes from the sensor or wiring.
- After repairs, monitor evaporator temperature and cabin airflow during A/C operation to confirm the reading responds normally.
Common fixes
- Clean and secure corroded sensor connector pins.
- Repair a signal wire short to ground or other damaged wiring.
- Replace the evaporator temperature sensor if it is internally shorted.
- Confirm normal A/C cooling and steady airflow after clearing the code.
Can I keep driving?
Normal driving is generally safe, but the A/C may cool poorly or the evaporator may ice over and reduce airflow. Switch off the A/C if airflow drops and arrange repair of the low sensor signal.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.