Guys, am trying hard to fix a problem in a series-6 (92-95)

Not getting an output on the 3E pin that triggers the #1 + #3 fan relay for normal cooling under normal conditions.

Have tried to force it active (Neg switched) by simulating the water temp sensor with a variable resistor & going through its entire range to simulate cold to hot.

Have changed the ECU, tested the fans with my own NEG signal.. All ok

Does anyone know the parameters that trigger the fan relay switch signal. Is it more than just the water temp sensor.......??

All other sensors & wiring is ok.

 

I am a new guy and have a FD. I do tune up and drive-ability at a general motors dealer and have done this for 20 years. I can only speak generally but I would surely look at the wiring from the coolant sensor to the engine computer for quality as well. I am assuming the computer driver grounds the circuit at a given temp but if the coolant sensor wiring is damaged/open/grounded it might not act as you expect. I would not think there are different inputs that would override the coolant sensor in any system. I would wonder if the engine has two coolant sensors or could you be testing the incorrect sensor. Keep applying pressure on the problem and it will give in.

 

DMRH,

Check the wiring to the water thermo-switch. When I was moving my harness around the connection to the water thermo-switch broke off at the wire - most likely due to lack of wire support and vibration over time.