How does the M50 coolant sensor work?

[Russell]

I am not sure how the coolant sensor really works. I know it is a float that drops when the coolant level is low. If low, the low coolant message is displayed.

However, when the sensor message is displayed, I think it means there is an electrical "open" vs a closed circuit with the message not displayed. Not sure?

Can someone help me understand it? I still get the message after replacing the sensor. I think itis an electrical issue and want to track it down.

Thanks

[AllanS]

I believe it works like this- when the coolant level in the expansion tank drops enough for the float to bottom out, the electrical connection is made, and the light comes on. On my old 525i, the light kept coming on for no reason, so I spliced the wires together, and had no more problems.

[Russell]

Uh Allan, when you connect the wires, I think the electrical connection is made. Therefore the sensor light should be "on" based on your description.

BTW, I took my old sensor apart. It seemed as if the electrical circuit is closed when the float is at the top because the two wires inside the sensor body were not insulated at the top (I think). I believe the float was part of the connection at that point because of the proxmity of the two wires and what appeared to metal on the float. I suspect that when the float drops, the circuit is open. However, I could be wrong.

I need to get a life and think about other things :)


I believe it works like this- when the coolant level in the expansion tank drops enough for the float to bottom out, the electrical connection is made, and the light comes on. On my old 525i, the light kept coming on for no reason, so I spliced the wires together, and had no more problems.

[AllanS]

When I connected the wires, the coolant level messages stopped- that's all I know for certain. If I were you I would just remove the sensor connector, and connect the leads with a small length of wire. That's probably the easiest way.

[Bill H.]

It is a simple job I did in the driveway. One wench difficulty :D

[Russell]

The problem is that the sensor message is still displayed which leads me to believe the problem is electrical. Also not as simple as you state (IMO) because of the tight space and coolant draining. BTW, what wrench did you use?


It is a simple job I did in the driveway. One wench difficulty :D

[Bill H.]

plyers (not really wrench). Not long ago Bill R. posted something about checking & soldering on the circuit board that controls this electric sensor. Check back a couple of weeks for that post...it may be your answer.
I had crossed my wires on the reinstall...try reverseing them. It worked for me. Good Luck. :p

[Russell]

Hey -sounds great will try!

[Javier]

the sensor and bridge with a copper cable the terminals at the connector socket (Leaving the sensor out of the picture). The alarm should go of. If not, there is something wrong in the circuit, otherwise, you have problems with your new sensor. May be the wire from the sensor to the CCM is opened, or the wire from the sensor to the ground is opened (or the ground connection loose).

To rough check, just unplug the CCM, and without removing the bridge in the sensor connector check continuity to ground from terminal 4 of X19 CCM connector. If you confirm continuity to ground from the Terminal 4 of connector X19 (Green) at CCM, there is something wrong in the CCM at the corresponding input, either an open sensing resistor, a cold soldering, or a similar bug. It is also possible a loose connection of pin 4 to the green socket.

Good luck.

[Russell]

Thanks - will check

[WarrenBrown]

I worked for a guy that replaced the sensor and the warning message didn't go out. We decided that the sensor was bad. I left that position before he resolved the issue.

There may be sensors that look alike but operate differently. Some cars, maybe not E34 cars have the sensor above the fluid level, our 525 has it below the fluid. These have to operate differently or the circuit is different.

Our fluid level is OK. Our warning message is not on. Disconnecting the level sensor causes the warning message to come on. With the fluid normal, I measure 2.5 ohms across the level switch.

Warren
91 318is
95 525iT

[harri525ixT]

logical behavior - everything is fine when sensor switch is closed,
and if either wiring is broken or the sensor opens due to low
level you get DING!.

oddly enough, I got DING!s when I accidentally overfilled the
expansion tank. which is sort of logical (COOLANT LEVEL instead
of LOW COOLANT LEVEL :). no more DING!s after I drained the
extra fluid.

another thing: does anyone have any idea on which CC module
pins the various burnt bulb warnings are connected? I get half a dozen
DING!s on cold weather (tail light, low beam, lic plate light,
brake light, ...), even though all lights work ok and the bulbs are
correct ones (and the connectors are clean, and the tail hatch
wiring is good).

thanks,
--
harri
-95 525ixTA