What it means
The evaporator temperature sensor signal voltage is above the upper diagnostic threshold. Typically open circuit or short to power.
How it works
The evaporator temperature sensor measures the temperature of the A/C evaporator so the climate control module can regulate cooling and help prevent the evaporator from icing over. P0538 sets when the sensor circuit reads above its upper diagnostic limit, which can happen if the sensor or its wiring is open or the signal is shorted to power.
Common causes
Most likely first.
- Sensor open internally
- Wiring open or disconnected
- 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
- Use a scan tool to check the stored and pending codes and freeze-frame data, then compare the evaporator temperature reading with cabin and ambient conditions.
- With the A/C off, inspect the evaporator sensor connector and accessible harness for disconnection, corrosion, damaged insulation, or loose pins.
- Check the sensor signal and reference or return circuits for an open or short to power, following the vehicle wiring diagram.
- Test the evaporator temperature sensor and its circuit against the manufacturer's diagnostic procedure to distinguish a failed sensor from a wiring fault.
- Repair the confirmed fault, clear the code, and verify that the live evaporator temperature reading responds plausibly as the A/C operates.
Common fixes
- Reconnect the sensor connector and secure any loose wiring.
- Clean or repair corroded, loose, or damaged connector terminals.
- Repair an open or shorted section of the sensor wiring.
- Replace the evaporator temperature sensor if it fails the manufacturer's test.
Can I keep driving?
You can usually drive if the vehicle otherwise operates normally, but the A/C may cool poorly or the evaporator may ice up and reduce airflow. Avoid relying on the A/C for demisting until it is working correctly.
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.