What it means
The auxiliary cooling system coolant temperature sensor A circuit has a detected fault. The module sets this code when the sensor signal or circuit does not meet its electrical monitoring criteria.
How it works
The auxiliary cooling system uses coolant temperature sensor A to report the temperature in that cooling circuit to the control module. The module checks the sensor’s electrical circuit for faults and sets P0E81 when its signal or wiring fails those checks.
Common causes
Most likely first.
- Failed coolant temperature sensor
- Open or shorted sensor wiring
- Loose or corroded connector
- Poor sensor ground or reference voltage
Symptoms
- Hybrid or EV warning light
- Temperature readings may be inaccurate
- Reduced power
- Cooling system may run inefficiently
How to diagnose it
- Read the freeze-frame data and auxiliary-coolant temperature readings to see when the sensor A circuit fault occurred.
- With the system safely cool, compare sensor A’s reading with other available temperature readings and the actual coolant temperature for an implausible value.
- Inspect sensor A’s connector and wiring for looseness, corrosion, moisture, chafing, or damage.
- Check the sensor circuit for an open, short, poor ground, or missing reference using the vehicle wiring information.
- If wiring and connections are sound, test sensor A against the manufacturer’s specification and replace it if it fails.
Common fixes
- Reconnect and secure sensor A’s connector.
- Repair damaged or corroded wiring and terminals in the sensor A circuit.
- Restore the sensor’s ground or reference connection if faulty.
- Replace auxiliary cooling system coolant temperature sensor A if it fails testing.
Can I keep driving?
A warning or reduced power can indicate that auxiliary cooling is not being managed correctly, so avoid strenuous driving or charging if the vehicle reports a temperature warning. Stop safely if a temperature warning appears or power drops significantly, and arrange diagnosis promptly.
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.