Fan runs immediately

[Skater]

I had a problem last year where the temp gauge stopped working. That problem fixed itself until it reappeared a couple days ago. I also noticed that the radiator cooling fan starts up as soon as the engine has started. I think the temperature sending unit (or whatever it's called) might be shot. Incidentally, the both problems fixed themselves simultaneously today, but I would like to fix the problem.
Two requests:
1) any suggestions to what the problem is.
2) Diagram to the temperature sending unit, or whatever the fan uses as a trigger to turn on.

Thanks.

[Ozzie]

What year?

[Willy]

Iem 7/8 is the pressure sensor, 7/16 is the temperature sensor.
The upper ECM is for diesel en 6 cylinder engines, the lower ECM is for the 5 cylinder petrol engine.
You can see that the fan is controlled by a transistor unit, item 4/71. This unit can fail or show
arratic behavior causing the fan to run while it shouldn't. The control unit can't be replaced alone,
it is part of the fan assembly. I am not sure that this is true for all MY's, but it is until MY2004.
Of course, failure of the fan control module isn't the only possible cause, but it is known to fail.
Willy

[Jim C.]

I've noticed a similar issue with my 2004 since the weather started getting warmer. The fan seems to rev pretty fast, then drops down to normal speed after a minute or two. It doesn't happen when I first start up in the morning, but only on subsequent starts during the day after it has been off a couple of hours. I've only had the car since November, so it may have been a pre-existing problem. I'll be taking the car in for a 105K service within the next week or so and was going to ask the technician about it.