What does it mean?
Vehicles with more than one coolant loop use several coolant temperature sensors, and this code refers to the third of them, which may sit in the radiator outlet, in an auxiliary or heater loop, or in a hybrid cooling circuit rather than in the cylinder head. The sensor is a thermistor: the module feeds it a fixed reference voltage through an internal resistor and reads the voltage that remains, which falls as the coolant gets hotter. This general circuit code is stored when the signal cannot be interpreted at all, in other words when the voltage sits outside the electrically valid window or disappears altogether. It points at the wiring, the connector or the sensor itself rather than at the cooling system, because the module has lost a usable reading before it can even judge plausibility.
Symptoms
- MIL (check engine lamp) on, sometimes with codes from other sensors that share the same reference or ground.
- Cooling fans running constantly at high speed, or not coming on when they should.
- Temperature gauge behaving oddly or staying at one end of its travel on vehicles that use this sensor for the display.
- Slower warm-up and weaker cabin heat because the module falls back to a substitute value.
- Higher fuel consumption while the engine stays in a default warm-up strategy.
- Readiness monitors that will not complete, so the vehicle is not ready for an emissions inspection.
Likely causes
- Open circuit in the signal or ground wire of coolant temperature sensor 3, often where the harness passes a bracket or a hot component.
- Corroded, spread or backed-out terminals in the sensor connector, frequently caused by coolant seeping along the wires.
- Failed thermistor inside the sensor, reading open or shorted internally.
- Signal wire shorted to ground or to another circuit in the same harness after chafing.
- Loss of the shared reference voltage feeding several sensors, which usually sets codes on more than one sensor at once.
- Water ingress into the connector, giving a resistance path that the module cannot interpret.
- Damaged pin or a failed input inside the control module.
How to fix it
- Read all coolant and intake temperature values on a fully cold engine; they should agree within a few degrees, and the faulty channel will usually sit at an extreme.
- Unplug the sensor and watch the reading: if it jumps to the coldest extreme the circuit is open beyond that point, and if it stays pegged the fault is between connector and module.
- Bridge the signal and ground pins at the connector with a jumper wire; a reading that swings to maximum temperature proves the harness and module are healthy and condemns the sensor.
- Measure the reference voltage and check the ground with a voltage drop test rather than a simple continuity check.
- Measure the sensor resistance at a known temperature and compare it with the specification table.
- Repair the harness or renew the sensor, taking care to seal the connector where coolant has been tracking.
- Clear the code, warm the engine from cold and confirm that the value rises smoothly and matches the other sensors.