What does it mean?
Coolant temperature sensor 3 is a negative temperature coefficient thermistor, so its resistance falls as it gets hotter and the voltage the module reads falls with it. This code is stored when that voltage drops below the lowest value the circuit can produce even with boiling coolant, which is an electrical impossibility rather than a real temperature. In practice the signal wire has found a path to ground, or the sensor has shorted internally. The module usually substitutes a default value and switches to a protective strategy, because a false hot reading would otherwise remove cold-start enrichment and leave the fans running continuously.
Symptoms
- Cooling fans running at full speed all the time, including on a completely cold engine.
- Temperature gauge sitting at the hot end or an overheating warning that does not match how the engine feels.
- Hard cold starting and rough running when cold, because the module removes warm-up enrichment.
- MIL (check engine lamp) on, often with the vehicle otherwise driveable.
- Weak cabin heat and, on some vehicles, reduced power as a protective measure.
- Noticeably higher fuel consumption in mixed driving.
Likely causes
- Signal wire for sensor 3 chafed through and shorted to ground against the engine, a bracket or the body.
- Thermistor shorted internally after age, vibration or coolant intrusion into the sensor body.
- Coolant or water in the connector bridging the signal terminal to the ground terminal.
- Harness damaged during previous work, with a wire trapped under a clamp or pierced by a cable tie.
- Signal wire touching another grounded circuit in the same loom after insulation has hardened next to a heat source.
- Failed input stage inside the control module, which is the last thing to suspect.
How to fix it
- Read the live value: a channel pegged at its maximum temperature with a cold engine confirms the short rather than a genuine reading.
- Unplug the sensor connector. If the reading swings to the coldest extreme, the short is inside the sensor; if it stays pegged hot, the signal wire is grounded somewhere in the harness.
- Inspect the connector for coolant intrusion, green corrosion and terminals that have been pushed back in the housing.
- Trace the signal wire along its route and look for chafing where it crosses brackets, the exhaust side or moving components.
- Measure the sensor resistance cold and compare it with the specification table; a value near zero confirms an internal short.
- Repair or reroute the damaged wiring, or renew the sensor, and seal the connector so coolant cannot track back into it.
- Clear the code and verify from a cold start that the reading rises from ambient in step with the other temperature sensors.