No primary fan--need help

[thegreatone]

I am unable to get the primary fan to run--without unplugging temp. sensor, I have replaced the sensor,relays and checked all wires! The secondary fan works OK-- it comes on when it reaches the red and also as soon as the AC is on. Once again if I un-plug the sensor they both come on!
Has anyone seen this?? OBviousely to computer can turn it on when the sensor is un-plugged!!

Has anyone ever heard of the PCM loosing the programming to turn on the primary fan?
Thanks for any info in advance,,enjoying the 9c1 life

:eh:

[capriceman]

In the under the hood fuse box, there are two fuses that controll the primary fan.
Fuse #12, 40amp is tied into the allways hot line for the secondary fan. The reason behind that is, if it is hot enough for the secondary fan to come on, You certianly need primary.
If the fuse should go out on the primary, the power for the secondary will operate the primary, saving the engine.
Check the primary cooling fan fuse in the under the hood fuse box. (10amp.)
If You unplug the sensor, the PCM thinks that the engine is REAL hot, and will kick in the secondary. Under heavier load, ie the a.c. being on, the PCM will try to prevent over heating by kicking in the secondary cooling fan. When the secondary kicks in, it sends rower to the primary fan if it needs it.
I've traced the circut, and that is the only thing that I can find that would create the symptoms that You have described.
Hope that it helps.

[reverendstu]

Same on my car, I think. Well maybe backwards. I've never seen the driver side fan come on by itself(without pulling the temp sensor), and the passenger side comes on when the A/C is turned on. I thought I would overheat when the gauge needle went into the red. I would switch on one of the A/C settings whenever the needle went too close to the red while stuck in traffic. One day I let the needle go all the way just to see if the car would overheat and well, it didn't. The car suddenly cooled down real quick. I pulled over and popped the hood, but only the passenger side fan was on, guess I missed the other one.
The fans are programmed to come on at fairly high temps, 225 for the primary(pass) and 232 for the secondary(driver), plus the sensor for the cheesy dash gauge is, I think, on the cylinder head but the one that talks to the computer is near the thermostat. I guess that's why everyone puts in a 160 stat and prog's the fans for 180 and 187ish.
Sorry for the long post, too much beer again!

[Incitatus]

I guess that's why everyone puts in a 160 stat and prog's the fans for 180 and 187ish
What is the benefit of running that much cooler? To prevent preignition?
I thought that was the purpose of the reverse coolant flow of the L99's and LT1's

[reverendstu]

D'oh, I forgot! Apart from not going to the edge of overheating all the time, and reducing stress, i don't remember the mechanical explanations. :confused: It is definitely a good mod , but for a real explanation I'd have to wade through all the posts on the other tech forums. Unless, of course, someone here can explain?