I have a W210 with 606 engine (99 E300 Turbo Diesel). Aux fans don't run ever and viscous fan roars after engine gets hot. I've jumpered 12v directly to the fans and they run full speed.

I've checked the codes on the A/C panel and there are no DTC error codes (A/C works fine). I've gone into the A/C sensor value display and accessed all of the sensor values. Everything looks normal including #20 which is the aux fan control current. Car when cold reads 3.2 and increases to 9 or so when engine warms up with A/C on but fans do not come on. I've done the "hold both AUTO buttons" until #20 value goes to max 21, but fans don't run.

I've found wiring diagrams but I'm having difficulty determining which fan module I have. I think it's either the N65/1 or the N76. I've located the module behind the drivers side headlight. The part number is 023 545 68 32.

Doe's any one know how to diagnose whether the module is bad or good?

I've been researching this for a week and I don't want to just shotgun parts, especially when they're around $200.

Thanks

You've not mentioned any temperatures; ... "after the engine gets hot" means what exactly? Running temperature? My aux fans aren't on at normal running temps.

Yes, running temperature.

My fans used to run with the A/C on and engine up to running temperature.

I've read that you can force the fans to run at high speed by holding in the two "auto" buttons until the #20 value changes to 21. I've done that and the fans don't ever run.

I'm looking for specific information on testing the auxiliary fan control module to rule out everything else.

The temperature sensor controls the speed of the fan. To test the controller and the fans you would need to simulate a resistance which represents the temperature. I had tested it with a 1k ohm potentiometer and found the temperature sensor was not working.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

All of the temperatures being reported by the climate control diagnostics are correct and reasonable. I am able to force the aux fan current output to high (#20) so that would over ride all of the temperature sensors.

All I'm looking for is a way to test the fan module directly with a volt/ohm meter. In other words, for example, "if the input voltage is x, then y voltage is applied to fan motor."

The input is a canbus message.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

You could unplug your fans and connect to +12:v. If they run maybe assume your controller is bad confused?

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Yup, did that. They run full speed with 12v connected directly.