I'm the original owner of an 02 R53. I'm in California and it's 110 degrees right now and I noticed that my radiator fan was not coming on with the brutal heat after stopping the car. I can hear the steering pump fan come on although when I connect the radiator fan plug directly to 12 volt power the low speed (stage 1) fan works, but the high speed (Stage 2) fan will not come on. I checked the fuses and they are all good. I read that if there is no low speed then its the surely the resistor, but I have low speed. I bought a cheap Amazon relay tester and it didn't seem to trigger the two large green fan relays so I bought an expensive relay tester and it did the same. Does anyone have any advise before I start buying things. Bad relays?

Appreciate the help.

 

Please note: this ONLY applies to pre-facelift (2001-2004) models, post-facelift have a DIFFERENT diagram.

The electrical diagram is highly confusing, because the way it works is highly confusing. Both for you and for future-me (because I just know I'll need it again sometime in the future), I've taken it from here and annotated it in 2 colors for low and high speed fan. Note that this is my understanding on it, but I'm not trained in electronics and might have understood something wrong (the way both low and high speed fan branch toward ground is strange to me). (updated thanks to @deepgrey explanations)


So if your low-speed fan works but high-speed fan doesn't work, it means:
- low-speed fan resistor is good (actually the most common failure as far as I know)
- you need to check both fuse FL05 (used for the signal) and FL11 (used for high speed fan power) in the engine bay fuse panel
- you need to check if the relay on the fan assembly itself works

To do that last step, rather than remove the fan (which is a bit time consuming, especially if it's your first time), what you can do (and I've done it myself, it works) is
- leave the 3 wire cables plugged (so that the fan does receive power via the big red/blue wire and is grounded via the blue cable)
- unplug the 2 wire cable from your fan (situated near the AC filler neck)
- put 12V through the 2 pins (polarity does not matter). It does not need to be from the battery, an external power supply providing 12V works just fine.
If the relay is working, the fan will spin. If the fan doesn't spin, the relay inside the fan assembly need replacement.

As for replacement, the official repair is to repair the whole assembly (fan + shround + low speed fan resistor + high speed fan relay). If you are handy, you can definitely replace just the relay itself. I have an old fan assembly in my garage if you need some pictures.

 

The diagram is actually pretty straightforward, but your annotations are incorrect. Fuse F05 is supplying +12 V to the low current control side of the two relays, and the DME is switching them to ground. That means all of your arrows on the control side are backwards (assuming you intend them to be current). Your ground circle is also strange. The blue wire there is positive, either +12 V for high speed or some lower value when being fed through the resistor, and X175 is a body ground, I believe.

Your troubleshooting explanation seems fine to me though.

 

Thanks so much for the detail. I will check the relay on the fan assembly via 12v.

 

Thanks, I was pretty sure I would get something wrong. I fixed those issues in the previous post so only the good information remains !