E39 Electrical and A/C issues... Related?

[CuyGuyE36]

Bought a 2003 525i manual sport package recently for $2300... Sweet car but it has some gremlins. Below is the run down to this point.

On the test drive I noticed that the ac did not work. Neither the compressor nor the aux fan will come on. I had the system evacuated and re charged and no change. All fuses including the under dash fuses are fine.

Meanwhile... The turn signals won't illuminate on the cluster, the cluster dimmer doesn't work, steering wheel controls don't work, radio doesn't work. I have also had a door sensor show as open when it is securely closed. Also the max ac button on the hvac panel doesn't work... All that said, I suspect it is a faulty ignition switch.

Here's where things get weird... I unplugged my battery when I got to work today and left it off for 6 hours... When I reconnected all of the above issues seemed to go away. Even the A/C seemed to work (90 degrees outside and cold air was coming from the vents) ... What a joyous moment.... But it only lasted for two minutes.

Has anyone experienced this? Have any ideas? Any help is much appreciated.

[BimmerBreaker]

Good chance the a/c issue is an aux fan related issue - either the fan itself, the harness plug or the pwm control wire. It does a self test on starting and if the fan fails that test the DME will disable the a/c system. If the fan works at next start the a/c may work.

There will be codes for this in INPA. The other problems can likely also be further diagnosed with INPA.

[shogun]

Moved to E39 forum from 5 general

[CuyGuyE36]

Good chance the a/c issue is an aux fan related issue - either the fan itself, the harness plug or the pwm control wire. It does a self test on starting and if the fan fails that test the DME will disable the a/c system. If the fan works at next start the a/c may work.

There will be codes for this in INPA. The other problems can likely also be further diagnosed with INPA.


So the aux fan failure shuts the whole system off, that is why my compressor clutch won't engage?

Is there a way to test the fan manually? Is there a way to test the compressor clutch? I tried jumping it but it would throw sparks every time.

[BimmerBreaker]

The compressor is controlled by the DME. If the aux fan test fails the DME will not engage anything in the A/C system.

You can test the fan in INPA.

[CuyGuyE36]

Need to pick one up. Any one in particular that you'd recommend? I've seen them from $30-$200 + ..

[BimmerBreaker]

INPA software is free just needs to be installed on an old laptop and you'll need the ~$20 cable to connect to the car. An "asus eee" laptop is cheap if you don't have an old laptop hanging around and it's a nice small size perfect for this purpose. It's what I've used for 8+ years.

[TiagE39]

You have a K-bus fault. The compressor, turn signals, inter-module communication, etc are handled by K-bus. The Dimmer is NOT K-bus (it is a direct connection to the LCM) but given that isn't functional either, this points to the LCM having a fault.

A K-bus fault (signal to ground, short, garbage telegrams) will cause the entire bus to shut down. All modules that rely on it for signaling (particularly on/off requests) will be unresponsive.

The LCM is one of the "Bus Masters" for K-bus on an E39, so all these symptoms point to a fault lying there.


So the aux fan failure shuts the whole system off, that is why my compressor clutch won't engage?

Actually no, the compressor will still run with a dead aux fan. Not very well however, you may lose cooling capacity when the car is at a standstill. The DME will disable the compressor when engine temp is too high (above 117F), full throttle is requested, running voltage is below 11.5v, or if the refrigerant pressure sensor indicates that the A/C system does not have enough refrigerant.

[CuyGuyE36]

So many electrical gremlins... Now my fuel gauge is acting up and my oil pressure sensor comes and goes. Also sometimes my tail light indicators will illuminate. All of these issues seem to come and go.

[CuyGuyE36]

So today once again the turn signals started working, the radio started working, and the ac and auxiliary fan started working for about 2 minutes. I must have a short somewhere?