Engine Coolant Temperature Sensor A
ECM is not receiving a proper signal from the coolant temperature sensor.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The Engine Control Module (ECM) relies on a coolant temperature sensor to monitor the engine's temperature. If this sensor fails or its wiring is damaged, the ECM can't accurately read how hot the engine is, which can lead to overheating or poor fuel economy.
What the computer is actually seeing
The ECM expects a voltage signal from the coolant temperature sensor that varies with temperature, typically between 0.5 to 4.5 volts. A reading outside of this range indicates a malfunction.
What a healthy reading looks like
Normal coolant temperature readings should correlate with the sensor signal: around 0.5V at -40°C, 2.5V at 90°C, and 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 and connectors for the coolant temperature sensor. Look for frayed wires or corrosion at the connectors.
- 2Using a multimeter, measure the voltage at the sensor with the engine at operating temperature. You should see a voltage of around 2.5 volts.
- 3If the voltage is out of range, remove the sensor and check resistance with a multimeter. At 90°C, it should be about 300-500 ohms.
- 4If the resistance isn't in range, replace the sensor. If the reading is normal, inspect the ECM for faults.
Common causes
- Faulty coolant temperature sensor
- Wiring or connector issues
- ECM malfunction
- Coolant leaks affecting sensor function
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's advisable to get it checked as soon as possible. Temporary drivability issues may occur.
Will this code come back if cleared?
Yes, if the fault is not resolved, the code will reappear.
Why is this code often seen with other SPN codes?
These codes may indicate related sensor or system failures that affect engine performance.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →