95 850 No Cooling Fan

Post by **Ozark Lee** » 23 Jun 2015, 00:38

abscate wrote:Absolutely. the ECU uses the engine temp to trigger fan operation - without the right input it may well default to putting the fan on full to save the engine.

Caveat - Im not an expert on the earlier ECU systems (or the later ones for that matter) but I believe the ECU controls this like my ME7 (1999)

It does. The ECT talks to the ECU and the ECU makes the decision on when to turn the fan on and at what speed. I have had the fan stay stuck on when I had a bad ECT sensor . A bad connector can do the same thing if the sensor resistance itself pretty much tracks the graph.

...Lee

Post by **polskamafia mjl** » 23 Jun 2015, 19:12

Thank you, Lee. I'll look into the ECT sensor and its connector.

Post by **polskamafia mjl** » 27 Apr 2016, 18:04

I just realized I never came back to close this thread out.

The problem was the plug for the ECT sensor. Age caused the plastic to crack and allow the electrical leads inside to move around. When it was plugged in the leads actually slid back enough to not make contact with the other end of the plug. As a result the ECU had no signal from the ECT. With a missing ECT signal the ECU will run the fan continuously.