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