BMW E46 cooling system components include:
- Radiator and coolant overflow tank
- Belt driven coolant pump bolted to the front of the engine block
- Electric cooling fan attached to rear of radiator -- the cooling fan is controlled by the engine control module (ECM) via an output final stage
- Automatic transmission models: Belt driven fan attached to front of coolant pump -- viscous clutch controls fan speed based on engine compartment temperature and rpms
- Electrically heated ECM-controlled thermostat
- Automatic transmission cooler (heat exchanger)
- Heater valve and heater core (for climate control)
- Coolant level sensor inside expansion tank
- Coolant temperature sensor at cylinder head
- Radiator outlet temperature sensor
- Coolant hoses and lines
The radiator outlet temperature sensor is located in the right side radiator hose. It monitors the coolant temperature as it leaves the radiator. The sensor reading is used by the engine management system (DME) to determine when the electric cooling fan is activated. The DME uses other inputs as well to control cooling fan operation and speed: coolant temperature at the cylinder head and AC operation.
If the radiator outlet temperature sensor fails electrically, a fault code is stored and the MIL (malfunction indicator lamp) is illuminated. The sensor can also leak coolant from the sensor sealing O-ring. I have replaced this sensor and soon after found a leak at the lower radiator hose. If it's in your budget, replace the lower radiator hose also as preventative maintenance.
Replacing the E46 radiator outlet temperature sensor is a snap and can be done working above the engine on the right side of your radiator. The sensor can be serviced from below also. You will have to raise and support the front of the vehicle on jack stands to do this.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.
Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
Drain cooling system. See our Pelican Parts Technical Article on Flushing Your Coolant. While working in the engine compartment at lower right side of the radiator, clean the area around your E46 radiator outlet temperature sensor.
If you are looking for more Technical Articles to diagnose or repair cooling issues please visit our E46 page.
Disconnect the radiator outlet temperature sensor electrical connector, (green arrow) (Radiator fan and shroud shown removed for clarity).
On the side of the sensor, there are two tabs you squeeze to release it from the lower radiator hose (green arrows).
Squeeze sensor release tabs and remove it from lower radiator hose.
When removing, check that the sealing o-ring does not remain in lower radiator hose (green arrow). If the o-ring remains in the lower hose, the new sensor will not seal and you will have a coolant leak.