94 Z28 cooling fan temp sensor location.

My cooling fans won't turn on when engine temp dictates they should. They work fine on start up and with A/C on. I need to know where the fan temp sensor is located.
Thanks in advance, Mossman
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I've had this same problem on my '94 Z28. My temporary solution was to run a ground switch to the cooling fan relay and have a toggle switch on the inside of the car. This was last fall and I had to put the car in storage and havent gotten it out and messed with it any more.
I found this on Alldata: Strategy Primary Cooling Fan (Fan 1) - The primary cooling fan is controlled by the PCM based on inputs from the A/C system, engine coolant temperature (ECT) sensor, vehicle speed sensor (VSS).
The PCM will turn the primary cooling fan "ON" when any of the following conditions exist at idle.
a.. Certain PCM diagnostic trouble codes (DTCs) set b.. ECT above 108C (226F) c.. A/C head pressure above 248 psi If the primary fan has been turned "ON" by the engine coolant temperature (ECT) sensor the PCM will turn the fan "OFF" when that temperature has dropped about 3C (5F). If the primary cooling fan has been turned "ON" by high A/C head pressure, the PCM will turn the fan "OFF" when the pressure has dropped to 208 psi. The minimum "ON" time for the primary cooling fan is 50 seconds.
Secondary Cooling Fan (Fan 2) (With A/C) - The secondary cooling fan is controlled by the PCM based on inputs from the A/C system, Engine Coolant Temperature (ECT) sensor, vehicle speed sensor (VSS).
The PCM will turn the secondary cooling fan "ON" when any of the following conditions exist at idle:
a.. Certain PCM diagnostic trouble codes (DTCs) set b.. ECT above 113C (235F) c.. A/C head pressure above 248 psi Once the secondary fan has been turned "ON" by the ECT, the PCM will turn the fan "OFF" when that temperature has dropped about 3C (5F). If the secondary cooling fan has been turned "ON" by high A/C head pressure, the PCM will turn the fan "OFF" when the pressure has dropped to 208 psi. The minimum "ON" time for the secondary cooling fan is 30 seconds.
According to the wiring diagram the PCM only sees the one coolant temp sensor and then decides to turn the fans on based on the strategys above. I know the Early production 94s use a slightly different system, but the basic operation is the same.
I think that based on this we both are looking at computers. $$$$$$$$$

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First of all, thanks for the reply. I appreciate your time.
Both fans (I crawled underneath and checked to be sure) turn on as soon as I turn on the A/C and shut off as soon as I turn off the a/c (no delay) This happens even when a/c had no freon charge (no head pressure), and cold engine. They run slower with the a/c on than when the high temp would kick them on making me think they are a 2 speed fan. On cold start-up the fans (both) screams for about 1 minute, then shut down. Currently when stuck in traffic, I turn the air on to cool it off. I don't know how many temp sensors there are on this thing and which one it would be, if I could even see it. I used to be an auto mechanic many years ago but I can't see or feel my way around this mess. Could be computer, could be sensor, but the sensor has to be cheaper and I'd replace it if I could find the right one. Then if it still failed to turn on, I'd take it to someone that knew what they were doing. I ordered the car in 94 ,to get the 6-speed, and only have 32K mile on it so I'd like to fix it right. I'd hate to take it to the stealership for a sensor but I may have to bite the bullet on this one. I don't know crap about the computer end of it.
Damn sure ain't like working on the old ones, But it sure gets better gas mileage..
Thanks again, Mossman snipped-for-privacy@comcast.net
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One more question I forgot in my reply,
Does the pcm use the same sensor as the temp gauge? If so, then the pcm must be the problem as the temp gauge works just fine. My question *assumed* two separate sensors.
Thanks again, Mossman
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According to the wiring diagram only one sensor is used. That is why I assumed PCM. if your gauge works, then the sensor should be working, and if you can turn on the fans with the ac, then the wiring and the relays and the fuses should be working.

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gorrilla wrote:

    Not true at all. It could be anything from a bad pin or socket, a damaged wire, a broke connection or something else. True the Computer maynot be getting a Signal from the sensor.
    Also my wisdom tells me 94 LT1 cars have both a CTS & a ETS. A Coolant Temp Sensor on the drivers front of the Intake Manifold. As well as a Engine Temp Sensor on the Rear of the Passengers side Cylinderhead. There is also a Third Temp Sensor. On the drivers side head at the water outlet.
    So before doing something stupid. Have someone do a computer diagnostic on it for which sensor is not reading with A/C off, engine past fan tunr on temp. I think even autozone can do this one for free.
Charles
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Still, according to the alldata website, which may or may not be accurate, the computer only sees one sensor and uses that data to turn on the fans. It also sees ac request and uses the same wires to ground the relays. I don't know if their information is accurate. I do know that is how 99% of OBDII vehicles operate their cooling fans. Like I said on my first post there is an early 94 production system that operates differently, and the info on that is no where near as good. If you don't have access to a good scan tool and schematic then you are probably better off taking it into the shop. But in my opinion, which you can feel free to take at face value, IF THERE IS REALLY JUST ONE SENSOR, and your gauge works and your fans come on with the ac, then it must be computer. The sensor is a simple thermistor and the comp can either read it or not.

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gorrilla wrote:

    See it's bull-shit statements like that, that cause me to have to take on more customers then I can handle. I don't know about YOU, but I have watched some of the brightest of the bright sit back and scratch their heads. Usually because they rush to change the parts first with out doing the diagnostic first. All in the rush to get it done in half or less of book time.
    In then last 4 years alone I have seen over a houndred wire & wire connection problems get blaimed on other stuff. Sometimes something as stupid as a correded pin & socket at the ignition coil acting like a bad magnetic pick up causing the injectors not to pulse. I have seen DIS systems not firing a clyinder right because of rust on the ground strap, yet only in one area, causing only one coil to act up, yet the other cylider off that coil to fire.
    Any more 60% of my business is fixing problems other people couldn't take the time to fix right. That's 60% I didn't want, or need. That 60% ties my shop up, and keeps my personial projects sitting on the waiting list, getting them pushed further and further back. Charles
Either do the Job right, or don't do it at all.
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whoa dude, I think you need to chill a little. I was just giving my opinion based on the data that I had. It was not meant as a personal attack on you. I said that I recommended seeing a professional with the proper resources, but told him what I expected him to be told. I didn't tell him to replace the computer. Remember, just advice....
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First off, thanks to both of you for your time and input. It seems that no matter what, I need some computer diagnostic scanning done.
From the beginning I *assumed" there had to be a hard wired, on/off sensor to trip the fans during something as serious as an overheated aluminum head engine. I found one coolant sensor right next to the thermostat I was replacing but my temp gauge worked so there had to be a secondary sensor. I found the one underneath by the water pump, but disconnecting this turned on my "service engine soon" light, making me believe it was working to some extent anyway. I'll get it scanned and post the results. It'll probably a couple of weeks til I get to it.
I believe my k&n filtercharger gives me just enough extra hp to run a flex fan. Where's the JB Weld?
Many thanks, Mossman,
wrote:

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The Coolant Temp sensor is mounted on the Water Pump. Drivers Lower area of the pump.
http://shbox.com/1/temp_sensor1.jpg
Excellent Reference page for future help; http://shbox.com/1/4th_gen_tech1.html
Tony
On Mon, 14 Mar 2005 16:27:20 -0500, Mossman

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