What does it mean?
Because coolant temperature sensor 3 is wired as a voltage divider, a rising signal voltage means rising resistance, and rising resistance means falling temperature. This code sets when the voltage climbs above the highest value the circuit could produce even in extreme cold, which no real coolant temperature can explain. The usual cause is an open circuit: a broken wire, a corroded terminal, a disconnected plug or a thermistor that has gone open internally. Less often the signal wire has picked up battery or reference voltage from a neighbouring circuit. The module substitutes a default temperature, which typically leaves fuelling richer than necessary and disables monitors that need a valid coolant reading.
Symptoms
- Temperature gauge that stays at the cold end no matter how long the engine runs, on vehicles that use this sensor for the display.
- Cooling fans running continuously as a default protection, or failing to switch on at all.
- Rich running with poor fuel economy, a strong exhaust smell and sometimes black smoke.
- Rough idle once the engine is fully warm, because the module keeps applying cold-engine fuelling.
- MIL (check engine lamp) on and readiness monitors that will not complete.
- Weak cabin heating and a longer than normal warm-up.
Likely causes
- Open circuit in the signal wire or in the sensor ground path, including a broken conductor inside intact insulation.
- Sensor connector unplugged, not fully latched, or with a terminal that has backed out of the housing.
- Thermistor open internally after thermal cycling or corrosion at the element.
- Corroded terminals with a resistive joint that adds voltage instead of passing the signal.
- Signal wire shorted to battery voltage or to a reference feed after chafing against another circuit.
- Poor common ground shared with other sensors, which usually brings additional codes with it.
- Failed input inside the control module, to be confirmed only after the harness has been proved.
How to fix it
- Read the live value first: a channel sitting at the lowest possible temperature on a warm engine confirms an open circuit rather than a real reading.
- With the ignition on, bridge the signal and ground pins at the sensor connector. If the reading swings to maximum temperature, the harness and module are good and the sensor is open.
- If the jumper changes nothing, measure the reference voltage at the connector and check the ground path with a voltage drop test.
- Inspect the connector for backed-out terminals, corrosion and coolant tracking, and check terminal tension with a matching pin.
- Check the signal wire for continuity all the way to the module connector and for an unwanted feed from an adjacent circuit.
- Repair the open or renew the sensor as the tests indicate, and protect the repaired section from heat and chafing.
- Clear the code and confirm on a full warm-up that the value tracks the other coolant sensors.