stoning_volcom

iTrader: (6)

ok well she is hot,.... and by that i do not mean good looking lol. ok down to business. bought a 98 camaro z28 a month ago, ( and may i say it is my fav car yet!) on the way home she through a rod straight through the block. I had rebuilt a ls1 and it was sitting in my garage so props. got it back in there running and all is good. while she sets the fans do not turn on. so obviously she gets hot while sitting, and since it is winter i am not to concerned but she will be getting driven pretty hard over the summer so i want to make sure she is good to go. why arent my fans turning on? nope not the relays checked them they are fine, checked the fuse, fine. the only thing is maybe its a bad sending unit? not allowing the fans to turn on

ls2-GTO

Only thing I can think of would be wiring/sending unit

stoning_volcom

iTrader: (6)

thanks for the input. that is what i was thinking. didnt think maybe the wiring is jacked? from the sending unit. hmm ill check

Indyjc

iTrader: (1)

Maybe a bad wire or bad pcm. If you have one of the tuner programs you should be able to turn the fans on. Having the same problem with my secondary fan not coming on, my tuner says the fan relay is good, it's either a bad wire or pcm.

Good luck

garygnu

also check and make sure all your grounds are tight .

1 FMF

iTrader: (1)

the fans are controlled by the PCM, not a sending unit. If you look up fan switch mod, you will find the pin #'s of the PCM for the two wires that come from the fan relays.
There are 3 fan relays, and two wires that go from two of them to the PCM.
When one of the wires is grounded by the pcm, the two radiator fans operate in series and are on low speed. when both wires get grounded by the pcm, the fans operate in parallel on full speed. The PCM turns them on low speed when coolant temp is 226F, and on high speed at 234F according to my 2002 service manual. And the pcm knows when to turn them on because it knows exact coolant temp via the coolant temp sending unit.
If the PCM does not turn the fans on, then either you have a bad fan relay which I believe will set a check engine light. And if one or both of the relay wires to pcm is broken that also should set a check engine light. Worst case is the driver/transistor in the PCM that switches those wires to ground is bad which means you need a new pcm to have that functionality, or you do the fan mod and switch them on manually.
My guess is either (a) you're not letting the coolant get hot enough, you need a scan tool that will report actual coolant temp to really know, or (b) your fan motors are bad or not wired properly- you did not mention you actually got the fans to run only that you checked the relays unless i misunderstand.

RARON455

iTrader: (35)

the fans are turned on by a ground signal from the PCM, it is set up for two speeds, low speed and high speed, when in low speed, a ground is sent to relay 1 which powers the fans on in series, causing a low speed, when the signal comes for high speed, then relay 2 and 3 come on, causing the fans to be powered in parallel which is high speed. here is a schematic hope this helps

leftcoaster

1998 Z28. Cooling fans stopped working. I have narrowed it down to: a bad ECT sensor, a bad wire from the sensor to PCM, or a bad PCM. Going to switch out the sensor and do a continuity check on the sensor wires tomorrow. I have physically unplugged the fan relay signal wires from the PCM and grounded them and the fans work. My question is: all of the fan wiring diagrams show the PCM grounding the fan wiring system to activate the fans after receiving a signal from the ECT sensor, is the grounding actually done internal to the PCM or is there another relay somewhere that physically does the ground switching?

myk

iTrader: (4)

I'll be watching this thread as the fans in my '97 Z stopped working as well. All relays are good, the fans turn on low and high when connected to battery power or the proper relays are grounded, and I don't see a problem with the wiring. I'm guessing ECT, I'm hoping it's not the PCM.

Meanwhile you guys can do what I did: install the SLP fan switch and control your cooling manually...

stoning_volcom

iTrader: (6)

for me everything was fine for some reason the high setting in the ecu was set to 232 so my friend and tuner knocked it down to 210 for the high fans. for me it was a tune issue for some unknown reason

The Alchemist

iTrader: (19)

I'm bringing this back, because I have an issue as well.

My fan won't work. I have a single fan, that I wired off both of the hot leads for the two fans and it worked fine for a few years now.

The other day, the fan wouldn't turn on. I checked the fan with 12v, and it runs, so no issue there. I got new relays, and no issue there.

The weird thing is I have HPtuners, and can command on each fan or both at the same time, and the fan will turn on and run for 3-4 seconds, but then shuts off.

I checked the pcm wire for the low speed fan, and it has issues. When I checked it to ground for continuity with the key off, it's OL as I'd expect, but when I turn on the key, it completes the circuit, but it's high resistance, which then drops when I command on the fan, which I also would expect, but after 3-4 seconds, the resistance goes back up, but not to OL.

Do I have a bad PCM?

alaska_guy

Sounds like possible bad ground if resistance is high.

The Alchemist

iTrader: (19)

Turns out it was a bad flash in the pcm. The week or so prior I had flashed in a new tune just changing a couple idle parameters, and I did a quick flash, and I guess it got messed up somehow. So yesterday out of a hunch, I flashed in the previous tune, and sure enough the fan kicked on at 180 degrees just like it is supposed to and stayed running.

So I have a spare relay now.