Pusher (aux) Fan runs with car off

Qsilver wrote in a post 5 reasons that your ECM makes the pusher (aux) fan run. He was the only one who clarified all possible problems that could cause an aux fan to run when it shouldn't. He also attached a great diagram along with his explanation. I tried PM'ing him but its been a couple days now and I need help to resolve this problem. Here is my story, my aux fan was running one morning when I woke up. Yes, the car had be sitting in my garage overnight and I heard the fan running at full speed and then stopped. Since, it runs when driving with the ac off and sometimes it runs long after the car has been shut off. I know that the fan could run up to minutes after the car has been turned off, but thats not my major problem. I haven't read anyone post on these forums with type of issue, 95% of aux fan problems is that they don't run. I replaced this pusher (aux) fan about a year ago, and yes I didn't buy the high dollar one, but the $150 unit. I regret that now. So, before I go replacing this damn thing again, I was wondering if someone could give me some troubleshooting tips to determine if its the aux fan or a sensor, switch, or ECM. I am electrician by trade and have troubleshot a lot. I do most repairs myself if all possible. I would appreciate any insight anyone has when the fan runs with the car off. 2003 530i engine M54

The fan responds to a pulsetrain signal from the engine computer. If you have a true RMS digital multimeter, you can pull the connector off when the fan is running, and measure the voltage at the lightweight wire. If zero, the controller on the fan is bad.

Edjack, to measure zero or a voltage I need a reference to ground. I see the green wire on the fan side which lines up with the black wire coming from the controller. Is the black wire a ground or neutral? Thanks,

Brown is ground,

... on all German machines, and is connected to the chassis.

Interesting problem. Next time you find it running with engine off, disconnect the temp sensor on the radiator outlet. If fan stops I'd clean connector if corroded and/or replace sensor. If you replace sensor be sure to get new oring. Can you measure the sensor's resistance hot and cold, and w/fan running and post?

1+ to pshovest,

The temp sensor in the lower rad hose is a common culprit.
About $25 item, it comes with new O-ring.

Unplugged the sensor (lower radiator hose) once before while the fan was running and the fan continued to run. Remember guys, in my first post, the damn fan was found running one morning parked in the garage after being parked the night before. And then it shut off by itself.

We remember, but you haven't told us which of the (5) QSilver causes you've ruled out, so we've started from scratch.

When fan runs w/engine off, does it seem to be at max speed?
Why did you replace the fan the first time? Same issue?

Need to determine if DME is commadning fan to run or if fan controller has shorted/failed causing fan to run. Rad outlet temp sensor and AC high side pressure sensor control fan via DME, but usually not with ignition switch off....unless there is another problem keeping DME powered. You can disconnect AC sensor to rule this out

Edjack's test will determine if fan is OK or not, but wiring is tough to reach. It might be simpler to disconnect the control wire from DME to fan to rule out DME as cause.

Originally Posted by vanceBMW

Unplugged the sensor (lower radiator hose) once before while the fan was running and the fan continued to run. Remember guys, in my first post, the damn fan was found running one morning parked in the garage after being parked the night before. And then it shut off by itself.

Originally Posted by vanceBMW

Qsilver wrote in a post 5 reasons that your ECM makes the pusher (aux) fan run. He was the only one who clarified all possible problems that could cause an aux fan to run when it shouldn't. He also attached a great diagram along with his explanation. I tried PM'ing him but its been a couple days now and I need help to resolve this problem. Here is my story, my aux fan was running one morning when I woke up. Yes, the car had be sitting in my garage overnight and I heard the fan running at full speed and then stopped. Since, it runs when driving with the ac off and sometimes it runs long after the car has been shut off. I know that the fan could run up to minutes after the car has been turned off, but thats not my major problem. I haven't read anyone post on these forums with type of issue, 95% of aux fan problems is that they don't run. I replaced this pusher (aux) fan about a year ago, and yes I didn't buy the high dollar one, but the $150 unit. I regret that now. So, before I go replacing this damn thing again, I was wondering if someone could give me some troubleshooting tips to determine if its the aux fan or a sensor, switch, or ECM. I am electrician by trade and have troubleshot a lot. I do most repairs myself if all possible. I would appreciate any insight anyone has when the fan runs with the car off. 2003 530i engine M54

But only for a minute or less, It has happened to me only once and I was pushing car. Never has it run overnight.in my case AC was NOT on.My car is 2000 528.

I replaced the first fan because it burned up. I believe I ruled out the lower radiator sensor/switch because when the fan was running with the car off I unplugged it and the fan kept running. The fan varies in speed from time to time, which is the weird part.

Originally Posted by vanceBMW

Qsilver wrote in a post 5 reasons that your ECM makes the pusher (aux) fan run. He was the only one who clarified all possible problems that could cause an aux fan to run when it shouldn't. He also attached a great diagram along with his explanation. I tried PM'ing him but its been a couple days now and I need help to resolve this problem. Here is my story, my aux fan was running one morning when I woke up. Yes, the car had be sitting in my garage overnight and I heard the fan running at full speed and then stopped. Since, it runs when driving with the ac off and sometimes it runs long after the car has been shut off. I know that the fan could run up to minutes after the car has been turned off, but thats not my major problem. I haven't read anyone post on these forums with type of issue, 95% of aux fan problems is that they don't run. I replaced this pusher (aux) fan about a year ago, and yes I didn't buy the high dollar one, but the $150 unit. I regret that now. So, before I go replacing this damn thing again, I was wondering if someone could give me some troubleshooting tips to determine if its the aux fan or a sensor, switch, or ECM. I am electrician by trade and have troubleshot a lot. I do most repairs myself if all possible. I would appreciate any insight anyone has when the fan runs with the car off. 2003 530i engine M54

did you solve this mystery? Mine started running on its own while I've been at work today. Someone came and told me my engine was making strange noise and I walked out to fan running full speed. I unplugged battery till I could do research. After lunch I plugged battery up and fan didn't switch on, So then I cranked car for a minute and fan kicked on immediately. As soon as it did I cut off engine and fan stayed on.

my car is 2000 528