1996 chevy lumina

radiator fan won’t run when engine is hot. fan motor, relay and wiring check good. relay coil has no ground but changing control module has no effect on problem. engine temp sensor is new and reads good on resistance check. also low coolant is lit on dash though that may be a separate problem.

The problem might be with the Powertrain Control Module.

The PCM is what controls the radiator fan relays.

Already tried another PCM with no change.

It could be wiring. The PCM reads an open circuit and that trips the response. First make sure the connector pins are not corroded. If they are OK and you still have a problem, check for a broken wire (open circuit) in the appropriate harness.

Already checked the wiring from engine temp sensor and relays to pcm as well as pcm grounds and reference voltages but I’ll recheck to make sure I didn’t miss anything.

I take it the fan is not getting power at all?

You said the relay coil gets no ground. I’m assuming the PCM toggles the ground to turn the fan on/off. What happens if you ground it manually?

To db4690- the fan isn’t getting voltage from the relay.
To cigroller- when I ground the relay it turns on and the fan runs okay. When the engine temp sensor reaches operating temperature the f\relay doesn’t activate. I tried another pcm with no change in symptoms and the wiring checked good on a resistance check.

I’d say that you’re left with either a coolant temp sensor to PCM communication problem or wiring for the ground problem. I’m guessing you checked the wiring with an ohmmeter for continuity/resistance. That’s the normal thing to do, but won’t catch all wiring problems. I would think about running some temporary extra jumpers for both connections and seeing if that changes anything. It would also be nice to be able to put a scantool on it to find out what the PCM actually sees in terms of coolant temp.

Agreed, but I don’t have a scantool at the moment. The wire jumpers is a good thought though; I’ll give that a try and see if I can scare up a scanner.