Correlation between poor engine performance and fan relay

[RougeTrooper]

2007 3.0 E70
This problem started last winter in February/March. Cold or Warm Engine, doesn’t matter. Between 0 – 80KM the car struggled to switch gears and revved very high as if struggling to switch between 2-3 and 4. Going uphill and the car struggled.

The problem was intermittent, happened for a few days and gone for a month.No errors in INPA.

Since I was at 150,000 miles (240,000KM) I decided to do some DIY tune up, fuel pump/integrated filter, air filter, spark plugs, techron. No effect.
3 weeks ago a “2nd issue” started. In traffic the car started to overheat intermittently. Turns out the fan was failing intermittently, my commute is mostly highway so it was not very apparent. Still no errors logged.

Finally, 2 weeks ago the issue became permanent and the fan never worked and acceleration remained poor permanently – cold or hot engine. Pulled codes and got the 2EFE error – Electric fan shorted.
After some troubleshooting, I discovered the issue was the fan relay located in the passenger fender. I ran a direct 12 volt as a test to the fan taping into the positive wire that fed the fan. (just connecting +ve/-ve wires will not kick off the fan).

Anyway, with the 12V tap, fan came to life, took it for a spin and acceleration was back. Disconnected the 12V wire tap, fan stopped working and sluggish acceleration resumed.
I have now replaced the relay (Part# 61 36 7 661 503), car feels like I did a tune up.


Question – how in the world can a fan relay cause the engine to perform so poorly even when cold?
My only guess is the relay signals to the ECU to moderate acceleration because it expects the engine to overheat at low speeds...

[smassey321]

I think your guess is correct. When I troubleshoot by disconnecting things, the ECU always seems to try to outsmart me.