jcmiley

Yeah, I did a search and did not find what I was looking for. My digital readout indicated temps in the 220 range but the fans still did not kick on. I can get them to come on by turning the AC on, but they will not kick on automatically.

I figured it was just a bad sensor feeding a relay, but all the sensor kits I find only go to 1995 AND the digital readout is working.

Any takers?

Jim

larryfs

sounds normal to me.

LT4BUD

Not normal for a 96 LT4....at 220 both fans should be running low speed even with the A/C off.....will jump to high speed at 228...

tomtom72

Is it possible that the relays may have a partial failure? There has to be a way to get the relays to be grounded...the ECM does the ground wire switching when it gets a temp signal that meets the "turn on" temp...then it grounds either the primary fan relay or the secondary fan relay according to what the coolant temp sensor is telling the ECM.

The primary fan on a 90 is programed to come on at about 190* or there abouts and the secondary is programed to come on over 211* I think? When the temps go below 200* the secondary shuts off and the primary shuts off at 190*, again I think.

Either the temp sensor is N/G or the ground circuit from the ECM to the relays is N/G or the ground terminal at the relays are N/G. I believe if you hook up a scan tool you can "see" the ECM ground the relays at the correct temps. You could try to make up a ground jumper and ground out the relays manually to see if the fans come on...if they don't then the relays are N/G. If they work when you ground them then you have to trace the ground back to the ECM. Or just pull the relays and have them tested to see if they work okay?

Sorry that's all I got.:o

Tom

Sorry I forgot this...on my scan tool, snap on MT2500(very old one ) it tells me the temps at fan activation and tells me if the fan relay responds to the ECM's call on a separate line. Like it gives the temp read out and then Primary Fan On...Y/N same for the secondary.

jcmiley

I'll check the relays tonight. I thought the fan relays from the AC control and the ECU were the same though? This is my first Vette and it just seems that in stop and go traffic it is way too hot. I've reached 230 at times, but it never seems to go above that.

Jim

LT4BUD

Yes there are three relays that control the fans as commanded by the PCM. So I think you fans & relays are probably ok.

There is a schematic is this thread.

http://forums.corvetteforum.com/show...=schematic+fan

jcmiley

Awesome link. Thank you very much. It looks like all is normal with my ride. I followed the troubleshooting steps and everything checked out OK. I'm suprised the fans don't come on until 234 degrees !

Oh well, if this is normal then so be it.

Thanks again,

Jim

jcmiley

The diagram on the above link did not indicate this. They definitely are not kicking on at 228; it hit 230 today before I chickened out and turned the AC on to get the fans running. The troubleshooting diagram indicates a cut on temp of 234.

Jim

LT4BUD

Only the first diagram is for a 1996.....less the markups.....so you are looking at a nonapplicable diagram where you see the 234...

These are the facts:

On a stock 1996 both fans always run together.......

Low speed on at 219F and off at 207F
High speed on at 228F and off at 214F

With A/C on they essentially are on continuously....

You do have a problem!!

jcmiley

Thanks for clarifying. Now on to figure out the problem. Hopefully it's just a relay, but I'm doubting after looking at the schematic. It's sounding more and more like an ECM.

Jim

~db~

Maybe you have a temp sensor not reporting properly. Sludge and contaminant build up can cause this. Is the coolant clean? Has the system been maintained? I personally don't care to have them run at factory settings so I have the PCM kick them on at 190

jcmiley

Is there a separate sensor that feeds the digital guage information? I assumed one sensor did the job completely? Also, how did you reprogram the ECU to turn them on at 190.

Thanks for taking care of the newby,

Jim

ALLT4

Check the fuses, if they're OK just sit it out and wait untill about 240 until you chicken out. Mine didn't used to come on until about 230 or 235 at times. That sucks ***** if you ask me. I stuck a 160 t-stat in, had the fans reprogramed and I'm happy as a pig in slop now. Make your own decision though, 230 before the fans come on is stupid if you ask me. The actual head temperature is much higher than that if you look at your gauge, more than likely it's around 260.

I really think Chevy screwed this whole cooling scheme up from the get go. YES an LT1 can run hotter, but not that freakin' hot!

Here's a better picture of that schem in that link without the WP circuit.

~db~

I'm not positive but I believe there is only one sensor for temp report. The guage info feeds from the PCM data. As far as the programming goes, you can either do a custom flash from a supporting member or buy a hypertech and utilize it like I do...just for fan control and tire size info.