Checking the thermal switch (BMW 3 Series E46)

The thermal switch is located at the bottom hose on the radiator. It turns on the electric fan when the coolant temperature reaches a certain value.

Verification conditions:

• The thermal switch must be checked if the electric fan does not work when the radiator is hot.
• If the lower radiator hose is warm, the thermostat is OK. If the thermostat is faulty, the thermal switch cannot turn on the fan because it is not warmed by the coolant.

Checking the thermal switch without removing it

1. Disconnect the thermal switch connector.

2. Connect both contacts on the plug with an auxiliary cable. If the fan now starts, the fault is in the thermal switch. Replace it. Secure the new thermal switch with a new sealing ring to a torque of 20 Nm.

3. If the switch does not work despite the jumper of the thermal switch, check the reliability of the connection of the plug to the fan motor and the reliability of the contact. Check the electric wires, relay and fan motor. Check the electrical components, refer to Chapter On-board electrical equipment.

Checking the removed thermal switch

4. The thermal switch can also be checked after removal. To do this, connect an ohmmeter to the switch contacts.



5. Immerse the thermal switch in hot water up to the thread level and measure the resistance. At a temperature of +93±2°C, the resistance should be 0 Ohm, at a temperature below +89°C, the resistance should be infinite.