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1993-97 Gen II Small Block V8

colling fan issue

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Old 05-07-2012, 11:12 AM   #1
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Default colling fan issue

the cooling fans in my 96 z28 are not working. i have a feeling they are not working at all. it has the usual symptoms of the coolant temp rising when not moving. took it in to school while we were in hvac class. got it to the point where we could jump where the relays where and the fan would kick on. so i know the actual fan is working. now the question is how exactly are the fans controlled? i know there are 3 relays that are involved in it but im not exactly sure how it all works and i would like to know before i start throwing parts at it.
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Old 05-07-2012, 11:42 AM   #2
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Why not test the relays to see if they are engaging? It's been a long time since I looked into this, but I think the fans have two grounds. One to the chassis and another which goes into the PCM. I believe the fans are also on a two speed system. I'd check/test the relays first before going any further.
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Old 05-07-2012, 01:36 PM   #3
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I figured there would be something i missed. Yes i did test the relays to see if they were engaging. Took them all out and put voltage to through the coil side and they all clicked like normal. What exactly controls the relays?
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Old 05-07-2012, 01:38 PM   #4
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I think a signal from the PCM, which in turn comes from the water pump temp sensor, however I believe if the sensor is not operating w/in it's parameters it will throw a SES light and turn the fans on. Do you have A/C hooked up? If so, have you turned it on to see if the fans engage? Not sure if shoebox has a schematic on his site for OBDII cooling fans. If not, a Haynes manual does.
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Old 05-07-2012, 01:42 PM   #5
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A/c has been removed. Except for the condenser and the evaporator. No ses lights either.
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Old 05-07-2012, 01:43 PM   #6
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Read my ninja edit.
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Old 05-07-2012, 04:32 PM   #7
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looked on shbox and it looks like the relays or the fusable link are the culprits. most likely not the fuseable link since the fan does work when the pins are jumped. so its either the relays or something up with the pcm/ ect
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Old 05-07-2012, 06:14 PM   #8
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ok so i checked all 3 relays by putting them in the fog spot and seeing if the fogs worked. all 3 worked fine. at this point i am lost and its most likely a sensor or something up with the pcm
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Old 05-07-2012, 09:17 PM   #9
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i continued to read on shbox and read about jumping pins 5 and 6 on the dlc i did and nothing happened. so it looks like the pcm is not communicating. or the is a bad ground somewhere
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Old 05-07-2012, 11:02 PM   #10
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I had the same problem on my 96 z28, the fans would not kick on at all, you need a new coolant temperature sensor that screws into the front of the water pump, NOT THE ONE FOR THE GAUGE! There about $10-$12 bucks at most part stores. That should fix your problem.
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Old 05-08-2012, 06:31 AM   #11
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I had the same problem on my 96 z28, the fans would not kick on at all, you need a new coolant temperature sensor that screws into the front of the water pump, NOT THE ONE FOR THE GAUGE! There about $10-$12 bucks at most part stores. That should fix your problem.
That's not the problem if he jumps pins 5 and 6 on the DLC and they don't come on. That bypasses any input that sensor would have.

OP, you need to see if you are getting a ground from the PCM to the green and blue relay control wires when you jump the DLC (and make sure you have the key ON after you jump it or it won't work).
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Old 05-11-2012, 10:33 AM   #12
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so i now feel like an idiot. the fans are coming on at the correct temp and the temp sensor is reading the right temp as far as the one in the wp. i guess the one for the gage is a little skewed and was throwing me off. and now for the next question. how do u go about lowering the temp that the fans come on? tuner? it just seems like the 230 mark is a little high for them to be kicking on even if the factory setting is for around that.
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Old 05-11-2012, 01:42 PM   #13
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Reprogramming the fan ON temps is a great way to handle it. Then there are no extra switches or wiring and you never have to worry about it.
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Old 09-22-2012, 05:49 PM   #14
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I posted my reply before I actually put the coolant temp sensor in, thought it would for sure fix my problem but it did not. Ive traced the blue and green wires all the way from the pcm to the relays and cant find anything wrong. Also when I jump the 5 and 6 pins on the dlc it only kicks on my fuel pump for a second it doesnt kick on my fans. I know the fans are good because I jump them in the relay box and they come on and the relays are good too??????? Im stumped, want to buy the SLP switch but dont have the $70, Ive been trying to figure these fans out for awhile, I need some help
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Old 09-22-2012, 05:49 PM
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