AUXILIARY COOLANT TEMPERATURE SENSOR A
Indicates an issue with the auxiliary coolant temperature sensor.
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What it means (plain English)
The auxiliary coolant temperature sensor measures the temperature of coolant in an additional system, usually for managing engine temperature and efficiency. If it's faulty, it sends incorrect readings to the engine control unit (ECU), affecting performance.
What the computer is actually seeing
The ECU expects a voltage signal from the auxiliary coolant sensor, which typically ranges from 0.5V at -40°C to 4.5V at 140°C. If the signal is out of this range or shows a consistent short or open circuit, it triggers this fault code.
What a healthy reading looks like
0.5V (at -40°C) to 4.5V (at 140°C).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the wiring harness and connectors for damage or corrosion. Repair if necessary.
- 2Test the voltage at the ICP (In-Cylinder Pressure) connector with the ignition on. You should see a voltage between 0.5V and 4.5V. If not, replace the sensor.
- 3Inspect the actual coolant level. Low coolant can affect sensor function. Refill if necessary.
- 4If voltage is normal, replace the auxiliary coolant temperature sensor and clear the code.
Common causes
- Faulty auxiliary coolant temperature sensor
- Wiring issues (shorts or open circuits)
- Bad connections or corroded terminals
- Coolant leaks affecting sensor readings
Typical repair cost
$$ - $$$
Related codes
Frequently asked questions
Is it safe to drive with this code present?
It's usually safe to drive, but overheating may occur. Monitor the temperature gauge.
Will this issue come back after fixing?
If the repair is done correctly, it shouldn't come back. Look for underlying issues in the wiring or coolant leaks.
What else might trigger this code?
Bad wiring or connector issues are common culprits, along with a failing sensor itself.
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