SAE J1939 Parameter Group 1: Engine Coolant Temperature Data Validity

The engine control module (ECM) is receiving a signal from the coolant temperature sensor that doesn't make sense, indicating a possible sensor fault or wiring issue.

The ECM expects a coolant temperature value indicating the engine's temperature, typically between 180°F and 220°F during normal operation. A signal outside this range, like a negative value or a voltage under 0.5V or over 4.5V, triggers this code.

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.

1. 11. Start with a visual inspection of the wiring and connectors going to the coolant temperature sensor. Look for signs of damage or corrosion.
2. 22. Check the coolant level in the reservoir; make sure it's at the recommended level and not leaking.
3. 33. Use a multimeter to measure the voltage at the coolant temperature sensor connector. It should be between 0.5V and 4.5V with the engine at operating temperature.
4. 44. If voltage is out of range, test the coolant temperature sensor by swapping it with a known good sensor. Read temperature values reliably via a scanner.
5. 55. If the replacement sensor works, then replace the faulty sensor and clear the DTC. If not, closely inspect wiring or replace the ECM.

• Faulty coolant temperature sensor
• Damaged wiring or connector to the coolant temperature sensor
• ECM failure or glitch

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