I have a 1990 IROC-Z (350/700R4). It has dual electric fans and the serpentine system setup. My fan relays are underneath the hood on the driver's side firewall. My primary cooling fan will NOT kick on when the car gets upto temperature. If I jumper the ALDL connector, it will kick on. If the secondary fan comes on because of the A/C, it will kick on. If I unhook the connector from the CTS, it will come on (a SES code will pop up also, because of the unhooked CTS). With that information, what does that 100% prove is good? Fan Motor? Relay(s)? Fuse(s)? Fusible Link(s)? ECM? Wiring? CTS? I have tried 2 new CTS's. I swapped in the secondary fan relay for the primary. Checked the 'FAN' fuse in the fusebox. Replaced some fuse on the passenger's side fender (Had no idea what it was, just thought it couldn't hurt). I haven't owned the car very long... under 2 months. The ECM looks very clean (maybe new). I have no idea if it is stock or not. I also have no clue if the EPROM (chip) or the fan swicth are stock. I think the fan switch only operates the secondary fan anyways. The secondary fan kicks on slightly before 230 degrees. I have read about 20 different messages about fans and 90% of them have different temperatures listed for when the fans should kick on. According to the FAQ on this website, it says for a 1990... the primary fan should kick on at 190 and the seconadry at 222. Is this correct? When should they kick back off? My car has been fine since I got it (2 months ago) until the other day. The temp gauge got to 250+. It also did this again, 3 days ago. On the highway, it runs 160. Usually 180-220 in town. Before the overheat, it never went above 230. I have no idea if the primary cooling fan problem was the cause or not? Is it possible, or would the secondary fan (only) keep the car below 250-260+ (even on 95 degree days while idling in place for several minutes)? Anyways, sorry about the LONG post. I just want my fan to work right. I searched the boards, and found a guy named 'sancho' with the same/similiar problem. I PMed him, but he never responded. I was hoping someone else could help.....

-Thanks

 

one fan should be enough to keep the car from overheating. i have my secondary fan hooked up to a manual switch and the temp rarely goes above 200 in traffic in 90* weather.

AFAIK the main fan should turn on at about 222* and the secondary fan at about 238*. i know that if i dont turn my secondary fan on, the ECM will turn on my main fan when the needle is around the 220* mark.

you could also have a problem in the wires somewhere.

i would get a wiring diagram and follow that. to me it makes it much easier when trying to diagnose PITA electrical stuff.

at least you can rule out the fan motor, relay and fuses.

 

hi,

i have the same car as you.

when my sendin unit for the fans quit, i just ran them to the radio power wire. so whenever the key is on, both fans are on. i had them hooked up to a toggle switch, but the switch would get REALLY hot and start to melt the wires.

well good luck.

 

I have the same problem. I think it's the switch in the pass side head. I didn't feel like changing it yet since it's a pain to get to with the smog and a/c stuff in the way so I wired up two switches to the grounds on the fan relays so I can turn on either one with the switches. I am running the primary all the time and it rarely gets past 160*.

 

llvll4l2c91350... If one fan is enough to keep the car from overheating, then why are there 2 ? And if you only need one fan to be alright, I must have another problem too As far as a wiring problem, I don't see how it could be??

prOject-IrOc... I see where you replied to another one of my messages saying that we have the same car That's cool, I love my car (most of the time, lol). Sorry, I don't have any pics yet.

Zepher... What switch are you talking about? The Coolant Temperature Sensor (CTS)? I have replaced it twice this week, with no luck

Note - I don't really want to hook up a manual switch or wire it to always be on. I would like to fix it the right way, if possible...

 

in case the main fan fails to turn on at 222*, that switch on the passenger side head (not the CTS) turns on the second fan at around 238* or so, preventing overheating.

 

I have also been told that it could be an ECM problem

 

How do I recognize if the ECM and EPROM are factory? How do I test them?

 

very good chance vader won't answer if you ask for him by name, read the sticky. 100% chance i won't answer even if i can if you ask for someone by name.

 

Ede... Okay, I edited my posts and removed any mention of Vader. The only reason I included his name in the first place was because I read other messages where he was discussing the same problem, and I thought it may seem rude or 'pushy' to PM or e-mail him.

 

Chuck: Sorry I didn't respond; I don't check my PM as often as I should.

Yes, it looks like you're having the same problem as I "was" having--almost to the letter. Based on what you have posted, and what I have experienced first-hand, I can say this much:
<ul>
<li> Your fan motor is good
<li> Your fuses are good
<li> Your relay is good
<li> The wiring between the battery, the relay, and the fan is good
<li> The wiring between the ECM and the relay is good (since invoking the diagnostic mode turned the fan on, as it should)
</ul>
The above, I have found, is actually what made this problem difficult, as that describes where the <b>vast</b> majority of fan problems arise. However, since we can be reasonably sure that it is all operating as it should, we need to look some where else...

A bad CTS would indeed cause the problems that you describe, but you say that you have tried two different (hopefully new) ones. The probability of getting two bad CTSs in a row is low enough that I would also say that your CTS is good as well. In my case, I ended up buying a new CTS, too. But when I tested my new CTS and old CTS side-by-side with a multimeter, I found that my old CTS was never bad to begin with.

That really leaves you with only two things, then: the ECM, and the wiring between the CTS and the ECM. However, when you say that disconnecting the CTS turns the fan off and sets an error code, that tells you that there must be some communication between the CTS and the ECM.

So, like I said, you seem to be having the same problem I was having, and you also seem to have covered the same bases that I have. When I got to where you are, however, I just broke down and bought a fan switch. It's not the way that I like to do things, but at least the fan gets turned on.

That's probably not the answer you were looking for--I, myself, am still somewhat "boggled" by this problem. I'd like to know if anybody else has some suggestions for you, because I bet it's the same problem I'm having.

If you really want to, you might try changing the ECM again. I know that, in my case, I was having this problem even with a new (remanufactured) ECM--but, then again, the ECM really is a whole bunch of variables that could go wrong. I also wonder if it's possible that your PROM might have been re-programmed with a different fan kick-in temp.

 

"However, when you say that disconnecting the CTS turns the fan OFF and sets an error code, that tells you that there must be some communication between the CTS and the ECM." - Sancho

Actually, it turns the fan ON not off. I'm assuming it's a 'fail-safe' feature to keep the engine from burning up, if the CTS goes out?

How could I test my CTS?

 

Chuck: Oops... sorry 'bout that. Yes, it makes more sense that the ECM kicks the fan ON rather than OFF.

RE: Testing the CTS... Vader did a better job of explaining it than I could. See this post and scroll down to Vader's post with the table titled "GM Coolant & Air Temperature Sensors". He explains it all there.

Of course, you will need a multimeter to test any of it. Per Vader's post, you also want to check for a 5 VDC (+/- ~0.3 VDC) reference signal across the harness connector.

If you have your old CTS (or one of your new ones) laying around somewhere, you might even want to just bench test those at varying temperatures to see if they are indeed "bad". Just set your multimeter to check resistance, check the resistance readings across the CTS terminals, and compare the results to that table. If the temperatures for the given resistances seem reasonable, then you likely have a well functioning CTS.

 

I had this same exact type of problem with my '89 IROC. My weakest area is electrical problems. I do have a 1989 genuine Chevrolet Camaro Shop Manual to help me out. I ended up tracing the ground wire for the primary fan all the way up into the ECM. The ECM was not grounding out the primary fan which is what it does to turn it on. On my '89 its a white striped green wire. The primary fan would kick on when I ground it out with a test wire. I could get the primary fan to kick on by grounding the green wire where it plugs into the ECM. Didn't feel like replacing the ECM just to get the fan to ground out. So I clipped a junction block on the green wire by the ECM and ran it to a toggle switch. Flipping the switch grounds out the fan and on she comes.

 

Are you sure this is the exact same problem? Would your fan kick on if you jumper the ALDL? What about when the aux. fan kicked on because of the A/C? And when you unplugged the CTS connector?

 

If the cooling fan will operate when the ALDL diagnostic request line is grounded, the ECM sinking output is working just fine. Your problem is elsewhere. Have you checked your Private Messages?

 

Vader... yes, I wrote you back. I don't see a 'B' on the relay. I wrote some other stuff too.

 

Your relay should have either a 'B' or 'F' terminal that is connected to the erlay operating coil. The primary fan should have a dark green/white wire connected to that terminal. Grounding that wire or terminal (with a jumper wire to ground) should operate the realy (and subsequently, the fan) whenever the ignition circuits are on.

 

This thing is killing me...

Okay, Vader... The green/white wire is NOT on 'B' or 'F', it IS on 'C'. I grounded 'C' and get nothing?!

I tested the CTS with a multimeter and it looks good acording to the chart. I am gonna pull the chip and see if perhaps it is something other than factory (I doubt it though, because the car was 100% stock when I got it).

-Thanks again

 

Both of my fans run when I jumper the aldl.

 

They do? I don't think there supposed to...?!

 

I am pretty sure they did, but I will double check tomorrow.
Also, I was able to get both fans to turn on with the a/c switch wire unplugged from the hi-pressure line.

 

Yeah, I can get both of mine on with the A/C switch also. I just can't get this goofy relay connector to 'ground' AAHHH!!!

 

Chuck: Sorry to take so long to reply--I've been on vacation. Have you found out anything new yet?

In response to your question: yes, as far as I can tell, I'm having the same problem as you. My primary fan did turn on when I jumpered the ALDL as it should and, as Vader said, that means that your ECM is "communicating" with the fan relay as it should. That really rules a lot of things out right there (which is why I never could fix the problem).

Also, my secondary fan does kick on with the A/C as it is supposed to. There is an A/C line pressure switch which activates the secondary relay when the A/C system pressurizes. The secondary fan is also controlled by a temperature switch in one of the cylinder heads, which kicks the fan on at something like 235 degrees (don't quote me on the temp).

Zepher: Only the primary fan is supposed to come on when the ALDL is jumpered. The only way that both would come on is if your engine was hot enough at the time you jumpered the ALDL that the secondary fan switch was activated. It almost sounds like both of your fans are hardwired to the same relay...

 

Car was hot when we jumpered the aldl. it was at 250.
Neither fan would come on at all at any temp.
I think both fans came on when the A/C switch connector was unplugged for a bit then the primary one turned off.
Right now I have two switches, one to the ground on each relay so I can turn on one or the other or both. I am running the primary all the time so I don't forget and kick on the secondary if I am in traffic and the temp rises. I too would like to get them working correctly.

 

I have had the same problem with my cooling system. I am running a dual fan setup, and have one of the fans set to be operated by the ECM at terminal C1. While the fan runs in diagnostic mode, the ECM never turns it on. I have tried resetting temp values in the PROM, tracing wiring, and everything else I could think of. After having a similar problem with my girlfriend's 1992 Lumina, I am convinced that the ECM's fan control circuitry is a weak link. The Lumina has one temperature controlled fan and one linked to the AC compressor, but both are operated through the ECM, as opposed to the F-body's secondary fan being hard-wired to the AC high presure switch. I could not get the fans to work in either situation, and eventually wired them to a manual switch. While having the ECM operate the fans would be a great convenience, I think the best thing to do is to get a Hypertech 160 degree switch and wire the grounds of both fan relays to it. I just hate spending $40 for what should be a $10 switch.

 

Is your car getting to operating temperature? 210-220d?

 

Mine gets to operating temperature and would readily go beyond if I did not shut off the A/C occasionally in standing traffic. I can run all day at 160 in 100 degree weather with the A/C on full blast as long as I am going at least 55, but as soon as I stop, the temp. gauge starts to climb. I've boiled it before. Seems to me like it should be doing better. I have two 12" fans moving about 2800 CFM, and a full size truck radiator rated for a 350.