I inherited a 3.8L 96 Regal. It gets hot in Austin, Tx so I need the primary coolant fan to turn on.
I've replace the relay, Temp Sensor, and thermostat but the primary coolant fan (Driver side) will not turn on. Both it and the secondary fan (passenger side) turn on if I disconnect the temp sensor so the path from the computer throught the relay to the fan must be ok. The Secondary fan does turn on if the temp guage gets up to 3/4 full (the guage is a mirror of the Fuel Guage). I beleive there is only the one sensor for the computer to read and turn on either or both fans. Isn't the Primary fan supposed to come on before the secondary?
What else can I check?
If I "hot wire" the primary fan the guage will stay below 1/2 so cooling works fine if I can just get the fan to turn on when it's supposed to.

sounds like a short to me! try turning on your a/c on high and see if both fans come on. One thing for sure, the fans are not bad themselves. try wiggling (sp) the wires and connection. If there is a short or loose connection you'll notice it.

When I switch to AC, only the secondary fan comes on.
Are both fans supposed to come on when the AC is on ???

There are no obvious wiring opens or shorts. But since both fans always come on when I disconnect the temp sensor, that tells me the wiring must be intact.

When I switch to AC, only the secondary fan comes on.
Are both fans supposed to come on when the AC is on ???

There are no obvious wiring opens or shorts. But since both fans always come on when I disconnect the temp sensor, that tells me the wiring must be intact.

Normally both fans turn on with A/C.

The fan turn on/off is controlled by the PCM module referencing to the ECT - engine coolant temperature sensor. From output of the PCM the signal goes to the cooling fan relays. When you unplug the ECT the cooling fans should both come on so that is normal. It is a fail safe in case the ECT goes bad. Something within the PCM like an output driver sounds like it is hung up.

BTW - Fan turn on temperature is around 225 degrees.

Thanks, But isn't it the same PCM output driver that successfully turns on the primary fan when I disconnect the sensor?

I wonder if the PCM is not reading the temp sensor correctly. The sensor path to ground is about 1350 ohms at 90 F and 350 ohms at 220 F. What if there is an additional 150 ohms of "bad" connection between the sensor and the PCM?
But that does not explain why the secondary fan, (which uses the same sensor reading as far as I can tell), DOES turn on.
Again, Should both fans turn on at once or is the primary supposed to turn on at a cooler temp than the secondary??

Thanks, But isn't it the same PCM output driver that successfully turns on the primary fan when I disconnect the sensor?

I wonder if the PCM is not reading the temp sensor correctly. The sensor path to ground is about 1350 ohms at 90 F and 350 ohms at 220 F. What if there is an additional 150 ohms of "bad" connection between the sensor and the PCM?
But that does not explain why the secondary fan, (which uses the same sensor reading as far as I can tell), DOES turn on.
Again, Should both fans turn on at once or is the primary supposed to turn on at a cooler temp than the secondary??

The 1350 ohms at 90 degrees appears good but it looks like the 220 degree resistance is high. At 212 degrees it should be around 177 ohms according to the calibration chart. So it does appear something is off or not linear by 150 ohms.

From what I can see in the SM both fans use the same temperature sensor but the difference is how the PCM is processing the input.

I'll check the rest once I get a chance.

I now believe the fans are working properly. I may have mixed up the 2 Fans.
The Passenger side fan turns on at 130 ohms (probably about 225-235 Degrees) and the Driver's side fan turns on at 115 ohms. I was never getting the engine hot enough to turn the Driver's side fan on.
I had to pull the passenger fan relay to get the engine hot enough but the Driver's side fan did come on when the gauge reached 3/4.

I still have 3 questions:
1) The Temp guage has to get to the 3/4 mark before both fans turn on. Is that correct? At that point, the engine still does NOT smell or look like it's overheating so maybe that's ok.
2) While driving, in stop and go traffic, the Temp gauge will move between 1/4 and 3/4. Is that normal? On all my other cars, the guage hardly moves after the engine is warm.
3) Only the passenger side fan turns on with the AC. Is that correct?

I now believe the fans are working properly. I may have mixed up the 2 Fans.
The Passenger side fan turns on at 130 ohms (probably about 225-235 Degrees) and the Driver's side fan turns on at 115 ohms. I was never getting the engine hot enough to turn the Driver's side fan on.
I had to pull the passenger fan relay to get the engine hot enough but the Driver's side fan did come on when the gauge reached 3/4.

I still have 3 questions:
1) The Temp guage has to get to the 3/4 mark before both fans turn on. Is that correct? At that point, the engine still does NOT smell or look like it's overheating so maybe that's ok.
2) While driving, in stop and go traffic, the Temp gauge will move between 1/4 and 3/4. Is that normal? On all my other cars, the guage hardly moves after the engine is warm.
3) Only the passenger side fan turns on with the AC. Is that correct?

I never trusted the analog gauge on the Instrument Panel. I've seen deviation at the gauge versus what the PCM module had off the engine coolant temperature sensor. If you have access to a good scanner like an Actron CP9145 or Autotap it will read out a temperature indication you can trust and normally it will be below what the gauge reads.

I am not sure about a '96 Regal but on '97 and up both fans turns on in a low speed condition with the A/C in Max.