VOLVO
ECM-1801 - Engine coolant temperature (ECT) sensor. Faulty signal
System
Engine Control Module (ECM)
Volvo models this fault code applies to
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 ECM reads the engine coolant temperature sensor. If the sensor signal does not change after the engine starts, or a fault is registered in its signal wire, fault code ECM-1801 is set. The fault may lie in the sensor, the thermostat or the connector.
Possible causes
- Defective engine coolant temperature sensor
- Defective thermostat
- Oxidation or a defective connector
- Open circuit or short circuit in the signal wire
What you can do
- 1Switch off the ignition and check the coolant temperature sensor connector for play and oxidation
- 2With a diagnostic tool, check in live data that the coolant temperature value rises as the engine warms up
- 3With a multimeter, check that the signal wire from the sensor is not broken and not shorted to ground or voltage
- 4A defective thermostat can keep the engine too cold, which looks like a sensor fault. Have a workshop check it
- 5If the fault remains after these checks, have a workshop replace the coolant temperature sensor
Symptoms you may notice3
- The engine coolant temperature warning lamp is lit all the time
- The coolant temperature gauge shows maximum
- The electric cooling fan keeps running for a while after the engine is switched off
General guidance for car owners. Diagnosis on the car can point to a different cause.