I'm repinning a harness making a 7730 from spare harnesses. All works except the cooling fan. I can't get it to trigger.

I've wired the relay as proper as I can determine. Power in on relay pin D and Ground come from the ECM E8. Heavy wire are A and E on relay.

Bench testing relay is ok. Wiring tests.

W/hen I run the 7730 on the bench reading the datastream I can get Fan Request ON for Fan 1, but nothing out on E8. No change whatsoever. So rely is not clicking. I'm at a loss. I'm assuming that I can just heat up the coolant sensor to the trigger point (which I did) and the ECM calls for Fan Request (which is does) ... but nothing changes on E8.

Tried different ECMs, stock and custom PROMs. Grounds all good. IGN good. I'm missing something really obvious.

Question ... if measuring E8 will ti show Ground when the FAN Request is ON?

 

The ECM provides a ground to activate the relay. So E8 should show +12 volts until it wants the fan to run, then ground. It has been a while since I've looked at the fan logic, but there may be a short delay between the time the ECM wants the cooling fan to run and when it activates the relay.

RBob.

 

In my bench tests, I heated the sensor small torch (slowly) and it would climb. And then it would drop. It maybe sat in "FAN REQUEST" for a few seconds. Not too long. Maybe there is a timer to prevent it from switching on and off when it gets close to the temp? I never waited all that long.