The problem that you're having with your car is identical to one I had with my 1995 E420. I replaced the aux fan resistor and the problem, and did Jim F's cooling mod, and now the problem is solved.

First check for continuity at the connection. My resistor had failed and broken contact entirely. The terminal at one end was corroded as well. If you get good continuity, then check for resistance. I think that this resistor, because it's a power resistor, is in the 2-6 ohm range - not sure though. If you get a reading above 10 ohms it's definitely bad.

Note that the resistor activates the fans at low speed only - high speed fan activation bypasses this resistor. Unfortunately - the high speed fans only come on at really high temperatures (higher than I'd ever like to see my car).

My mechanic friend said that he's seen dozens of these things fail. It took me about 1.5 hours to replace mine (but it should be easier for you - the E420 resistor is really buried in the engine bay - like everything else).

Good luck

Troy 1995 E420

Awesome, thx for the tips, I'll go try it out.

As for Jim's resistor Mod, he specifies for a V8, I don't know where the ECT module is located in my 6 cylinder. Any ideas?

Hi Niko,

A very simple way to find out if there is really something wrong other than your electric fans would be to wire the connection to turn them on to high temporarily the next time you use the car. With both fans running high, check if your temperature still reaches 105 with the aircon off while using the car in stop and go traffic. Do the same with the aircon on. If you do not reach 105 with both fans running high all the time then all you probably need is a resistor or JimFs device to turn the fans on sooner then it previously did. I live in a tropical country and when my aircon is on and just 15 minutes of being in heavy traffic used to cause my temp to rise to 110 easily then the fans would kick in but by this time, the engine is already very hot coupled with the very hot outside temperature, even with both fans kicking in at this point it would take a long long time to bring the temperature down. The solution to my problem was to tropicalize my thermostat which opened at 65 deg, fan clutch which engaged at 90 deg and electric fans which engaged in high at 90 deg. I even installed a switch which could activate the electric fans to high from the dashboard. This is very usefull for very steep uphill climbs and after very high speed highway runs and during summer heat waves. With this setup, even with the aircon on and very hot midday temparatures, my temperature never exceeds 95 deg.
Hope this helps.