VOLVO
EFI-0021 - Engine coolant temperature (ECT) sensor. Faulty signal
System
Electronic Fuel Injection (EFI)
Volvo models this fault code applies to
This fault code has different meanings depending on model, model year or engine. Select the meaning that applies to your car.
Applies to the following models:
2 modelsS40 (1996–2004), V40 (1996–2004)
Show models by year and engine (2)
What does this fault code mean?
The engine coolant temperature sensor sends the engine control module a signal about the coolant temperature. If that signal is faulty, the code is set. The fault may be a defective sensor, a short-circuit or open circuit in the signal wire, or contact resistance in the connectors.
Possible causes
- Defective engine coolant temperature (ECT) sensor
- Signal wire short-circuited to ground or supply voltage
- Open circuit in the signal wire
- Contact resistance
What you can do
- 1Warm the engine up at idle until it is hot. With a diagnostic tool you can read the engine temperature in live data.
- 2Check the connectors to the coolant temperature sensor and the control module for contact resistance and oxidation, and remedy them.
- 3Check that the sensor is not damaged. Look for chafed wires or loose connectors, and see whether the fault appears when the wiring is moved.
- 4If no fault is found, the sensor needs replacing. Have a workshop do this.
Symptoms you may notice3
- The malfunction indicator lamp lights up
- The electric cooling fan keeps running after the engine is switched off
- Poor performance
General guidance for car owners. Diagnosis on the car can point to a different cause.