1999 323i Aux Fan Issue - Technical answers needed

I’d normally agree to that, but I can across something fairly unsettling today whilst probing for some answers. I threw the multimeter in high gear and checked the resistance of the fan control wire and came across 3.4 MegaOhms of resistance… That sounds like a lot for what’s supposed to be a straight shot of wire. I’m guessing somewhere in my harness there’s a problem of somewhat small proportions that could turn into a vehicle frying adventure of epic proportions.

From looking at the wiring diagram of the cooling circuit and the pinout of the DME I found that Pin 4 of the 40 pin off the DME is the fan control wire and it should be a straight shot of wire. I guess it’s taking a detour somewhere… If it’s taking a detoure into a power wire then no wonder the fan control portion of ther DME is roached. Ugh, more fun to come.

If the wire is open the fan won’t work. So how do you know the DME is fried?

Right on, good observation. I foud out in a few different steps. I checked the wire for continuity/resistance and then checked the operation of the fan control pulse at the pin directly on the DME. What I got was a whole lot of nothing exceptfor a very small amount of voltage, which could be back feeding through the circuit. That’s what I Think is happening.

If you are trying to measure a PWM signal it will only be a 1-3V on a regular multimeter.

Right, the signal I was getting at the DME was about 0.4V and the signal at the fan was about 0.8V, strange I know. On the other hand I was reading nothing at all when reading hz.

I’d fix the wire and than see what happens.

That’s probably the first thing I’ll do before I grab the DME. I’m just worried about something… I threw the probe in the fan control wire whilst plugged into the fan and it was showing that I was getting back voltage. I believe it was only throwing voltage when I had the fan plugged in so you may be on to something there! Fix the short then check the result for sure… I’m still ripping the front and rear ends off though, lol! I have a tear in the rear sub frame and some things I’d like to check/replace/clean/lubricate while the motor and trans and font end are off the car.

Just in case anyone is interested in the fix:

I fixed the wire which was worn through outside the care and then hooked up the factory fan. Turn out the factory fan was smoked and I replaced it with a new one. All said and done it only cost 400 buck for the new fan and some heat shrink and solder. Just plain simple.

If you weren’t so busy ICEing people, you would’ve figured this out sooner.

LOL! It was the ICE in the bag of wood that gave me the motivation to fix the wire! Also, on a side note, the ICE under my wiper helped out too!

ICE ICE BABY!