I have read a ton of forums and came up with some questions with my fans not working. Here is what I know...

1. Car boils over once gauge shows high or in red
2. jumped the DLC and did nothing
3. Fans work when connected directly to battery
4. Relays work fine (used Haynes manual for testing info)
5. Fans both come on with AC on
6. DTC reader shows no problems but does not give me any info on temperatures.

One problem found. According to Haynes,

Pin 1 = power
Pin 5 = no power (POWER ONLY WITH KEY ON)

Im getting the following with NO key on

Relay #1

Pin 1= power
Pin 5= power

Relay #2

Pin 1= no power
Pin 5= power

Relay #3

Pin 1= no power
Pin 5= power

Something there isn't right with power to relays.

Can I test from the wiring harness where we tap in to do a fan switch bypass? Im going to do the fan switch bypass but would like to get the fans working the way they are supposed to before going the switch way.
Also is there a way to jumper in where the relays are to turn on the fans?

Any help appreciated

Oxy

 

If the fans come on with A/C then the control lines to the relays are obviously NOT the problem.

So the logical first question is what temperature is the PCM seeing? As in could the ECT be incorrect?

 

i just had this happen ..on the water pump their is a sensor it tells the fans when to come on. it probably went bad . also when you take it out coolant will come out .so make sure the car has cooled .and after you get
done make sure to bleed the air out of the system

 

Power to the pins you show are exactly correct for a 1996. There is no problem there. As Speedy says, your circuitry is working just fine. Get a real scanner to check the temp.

 

Agree with above statements. The dash gauge is controlled by a different sensor than the fan gauge. The ECM uses a totally different sensor than your dash to determine when to turn on the fans. The fact that you can't see the temps. when you scan the computer points to this as being the problem. Just because a DTC hasn't been set should not rule out this sensor as being bad. The fact that the fans work, and the relays are closing means the fuses (fusible links as well) are intact.

I believe the ECM temp. gauge is on the water pump...but it's been awhile.

Test or replace.

 

The reason he could not see the temps was that he was using a code reader and not a scanner.

 

I had a feeling I was going to be told to use a scanner. Im surprised that the values for the relays are correct yet my Haynes manual doesn't say anything about being different for the 96's. I would take your word on that shoebox. I'm going to test the sensor see what it shows. If that pans out then I will get it scanned.

I have found the gauge and yes it is on the water pump. Its actually not all that hard to get to once you remove the air intake tubes.

The thing that gets me is when I do the DLC jumper wire should it not turn on no matter what?

Oxy

 

Check the wires to the ECT sensor. They are located in a warzone of wind, leaks, and pressure washes. They will deteriorate after time due broken wires, corroded terminals, bent pins, etc. A new pigtail from GM is $30-40. If you can find the terminal pins then you can just snip a few inches back and reuse your existing terminal.

 

If I remember right, I took a quick look and it seemed pretty good. I checked it when I had the IAT sensor out and checked that too while it was out. (IAT has nothing to do with the fans) Also the power coming to the pig tail for the ECT sensor was about 5 volts.

Im going to crawl under the car and see if I can test the sensor cold then hot when its in the pump. I really dont want to have to drain the coolant and all that if I dont need to.