I was pulling the codes off my 38-pin connector. I had the ignition switch on (engine off) and I happened to be calling for warm air on the heater (it was 42 F outside). I could hear some noise coming from my heater recirc pump. Then, for no apparent reason, both aux fans kicked into high. The coolant temp was right at 85C. Now, even with the ignition off, the fans will stay in high. I had to pull the 30A strip fuse out in order to get them to stop. I checked the resistance across the coolant temperature sensor at 85C and it was .51 K Ohms, which I believe is 510 Ohms. I know the normal resistance across the sensor is 310 Ohms at 100 C and 250 Ohms at 107C.

Does this sound like a bad sensor or is there something I'm missing here. Even with a bad sensor, it doesn't make sense that they will come on with the ignition switch off. Any ideas? Stuck relay, somewhere?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I checked it out again when the car was completely cool. When I put the 30A strip fuse back in, the fans ran on high--even with the key off. I measured the voltage going to the coolant temperature sensor on the intake manifold and, with the key on, it shows 5V. With the key off, it shows no volts. There is a continuous 12V running across the 30A strip fuse even with the key off. Anyone?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I changed the aux fan relay and it seemed to fix the problem. Maybe it was sticking.

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles