New Rad. Fan Sensor Doesn't Work?

[weste46]

Hello.
We recently bought a 318ti, and have had some issues with it. The radiator fan would not turn on when we first got it without the AC on. I jumped the trigger circuit for the fan at the radiator temperature sensor plug, and it worked both on high speed and low speed. Assuming the sensor was dead, I bought a new Facet sensor. Driving the car today with the new sensor, the fan never kicked on itself, reaching 216F without even low-speed.

Knowing that the circuit itself works (jumping ground and low-speed, and ground and high-speed), what else could cause this? Certainly nothing downstream of the sensor since the circuit is otherwise working. Perhaps a radiator blockage is preventing the sensor from reaching the temperature it needs to? I know the block sensor (which is what my OBDII scanner reads from) will be hotter than the radiator, but once the block hits 216F you would think the radiator fan would have at LEAST kicked in on low-speed.

If anyone has info on this please help! Thanks!

[MauiM3Mania]

Moved from BMW General Discussion sub-forum.

[bmwdirtracer]

Since the fan comes on when you jumper the sensor plug, either the new fan switch (red temp sensor) is bad, or the engine coolant temp sensor in the head is bad, or your OBD reader is bad. I wouldn't trust your OBD reader as far as I could throw it, personally. I'd have to recommend starting by reading the ACTUAL temperatures with an infra-red temperature gun, at the upper hose and radiator header tank, and lower hose, and thermostat housing. Metal temps will always read higher than hose temps; the black rubber hose or black plastic header tank is usually more correct.

Are you sure that you got the correct fan switch, for a 318, rather than a 325?

[weste46]

So now when I jumper the plug, the normal speed circuit does not work, and the high speed does.
I have jumpered the low-speed relay power and the fan worked. This tells me that the ground wire from the double-temp switch to the DME or DME to normal speed relay is bad.
I will run a new ground wire directly from the low-temp side of the double-temp switch to the normal speed relay. This should fix my issue.

[bmwdirtracer]

Have you considered the more likely possibility that the Normal Speed Relay is bad? You jumpered the power, rather than delivering a ground to pin 85 of the relay. Of course, fuse 16 might also be bad; it delivers power to the activation side of the relay....again, unaffected by your jumpering pin 30 to pin 87.

http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

[weste46]

I forgot to update this,

Making a new ground for the low-temp side of the double-temp switch fixed my issue. Everything works as it should now.