Quote:
Originally Posted by X5chemist
The fan does not start up when I pull the sensor off the coolant line. So I guess my sensor is toast. Time to drain the coolant and replace it.  |
Just trying to add some accuracy here, copying from my notes back when debugging my failed aux fan on my 2001 3.0i (same fan on all gas-engined E53s) ...
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Pulling the connector off the coolant temp sensor on the lower radiator hose will not turn the fan on. As detailed below, the ECU considers that to be a temp of -54*F, so not hot at all, so no need for the fan.
This has nothing to do with the temp gauge in the instrument panel. No warnings result when the temp varies to extremes.
Tests done with ignition ON, engine not running, battery charger maintaining voltage.
I used the foxwell to monitor live data on that temperature. Measured about 71F (ambient temp) when starting.
Disconnected the connector, simulating infinite resistance ==> -54*F
Measured resistance of the sender = 2.8 kOhms
Put the following resistors across the connector to simulate different temperatures:
temp [F] resistance [kOhms]
-54 infinity (unplugged)
71 2.8 (actual sensor)
94 1.48
122 0.80
159 0.40
213 0.151
241 0.100
These were done to confirm how I could simulate an overheated radiator hose, to hopefully trigger the fan to turn. Interweb lore says that you can just unplug the sensor, but that does not seem to work, which makes sense.
The 100 Ohm resistor simulates 241F, and successfully triggers the fan to come on (the command comes [command voltage signal drops], even though the fan did not spin while I was doing these tests - because my fan was broken).
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Pulling the connector off the AC pressure sensor, nearby, while the AC is turned on and the engine running, the aux fan should spin. More specifically as I tested it on my car:
(AC pressure sensor voltages given in an earlier post in this thread)
When the AC was turned on, the fan control signal dropped from its normal (fan off) state of 14V to 12 .. 11V, as before.
When the AC pressure sensor connector was removed, it very quickly ramped down, at about one Volt per second, ending at about 2.0V, which should be almost top speed for the fan.