Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
So.....you never checked the fan control module?
I am not sure why you are trying to keep engine at 80C. Thermostat does not begin to open until 87C. Rigging ECT will result in CEL.Thanks for the nice diagram. Power checks was the first thing I did when I initially realized the issue with the fan. Both permanent ground, hot-wire and 2nd hot wire (switched when the key is moved to accessories) all good. I initially didn't understand PWM fans, after dealing with this car, I understood the technology. Now with all the diagnostics I have done, I think the fan is working as expected.
The issue is fan demand being zero. Based on your diagram, the coolant sensor is good, tested another new one as well ($10 original from eBay). Not sure with ECU, what is the trigger condition for it put demand on fan. Since, A/C is shot, I cannot try A/C load anymore.
I may have to eventually use a secondary thermal sensor to cut-off original thermal sensor input at 80 degrees and which will force the fan to run (I know my gauge will show zero while fan is running).
Which is exactly why MB re oriented the Plug like this on later Cars :-I should have been more clear in my post. The male connector has seal around it, however, the female connector of the control module itself is not water proof.