1991 Camaro RS V6 3.1 - The fan not coming on...

I have tested the fan with direct power and it runs.

I have changed the Coolant Temp Sensor on the front of the engine



I also changed the Fan Relay on the drivers side firewall



and the fan still does not kick on when the engine gets hot.

I grounded the green wire to the relay and the relay clicks and the fan comes on. To me, this shows that the fan, the relay and the wires from the relay to the fan are good.

So, does this mean the coolant temp sensor I just bought is bad? or perhaps a bad wire between the sensor and the relay?

Rick

Seems like the ECM is not "seeing" the temperature.
You could disconnect the ECM and the coolant sender wires and measure continuity between the yellow wire on the sender connector and the yellow wire on pin E16 on the C3 connector of the ECM.

If that checks out, I'd connect the sender and measure the resistance between ECM connector pins E16 (yellow wire on C3) and B6 (black wire on C1). Let us know what resistance you found. I cant' remember off top of my head what the spec is. Something like 22k for room temperature, I believe. Up to 4k for fully warm engine. But I can't guarantee these numbers right now.

Actually, another possibility is that green/white wire from the relay to the ECM has a problem. Again, with disconnected ECM, ground pin E8 on the C3 connector of the ECM harness. With the key ON. If the fans come on, that circuit is ok.

If you have access to a scanner tool, you can hook it up to your car and see what temps the ECM sees from the sender and what the turn-on and turn-off temperature constants are.

Hope this helps.
Lou

Any update on this issue yet?

Lou

Im not sure about the V6 but the V8s have 2 coolant temp sensors. I had the same problem as you ans a mechanic told me to replace the other coolant temp sensor which, for me, is in the passenger head. When you are under the car it is by the starter. I am not 100% certain if it will work as I have not done it yet. Just in case here is a part number for the lower one. Summit Racing JET-60600 $38.69

Hope this helps

All our V6 and V8 engines have only one cooling fan switch. It's exactly the one you're talking about, on the passenger side just under the last two spark plugs.

The other sensors are not switches but sensors. There are usually two more, one for the computer, one for the gauge. They are on the front of the intake and in the driver side head (just below the first two spark plugs).

Hope this helps.
Lou

Ahhh I see. Learn something everyday.

is the one on passenger side the one that controls fan on and off temp? mine hits 220 with 185 stat and then fan clicks on sometimes i hit heat too. is the said sensor possable solution?

BigBadLou, great info Thank You,

any idea on what the sensor in the passenger side head does?

That is the one that tells the ECM what the temp is and controls the primary fan.
There are no body grounds on the fan relays. I just spent 2 days chasing my tail on a primary fan that ran when the key was turned on. I am using a 1988 firebird in a 89 Z28 that somebody butchered and there was a ring eye on a relay so I grounded it and that was the problem because the ECM uses ground to control the fans.