Im having problems with my fans on my swap. I know the fans work because when i uploaded my tune to the computer they both turned on. anytime you plug anyting into the diag connector they turn on. But they wont turn on as a result of heat. Where should i look?

 

i'm not an lt1 guy, but if you have fans turning on at diag, that means your ground to the relay is good, the relays and fuses are good, and that you have line continuity through the motor. I would investigate the coolant sensor itself. did you see fan 1 circuit or fan 2 circuit codes when you hooked up the diag?

 

I never scanned for codes after the engine was actually running. I dont have access to a scanner now. I get a coolant reading on my guage. could the sensor still be faulty?

Both my coolant sensors are brand new.

 

the system is pretty simple as far as components goes. temp sensor in block says its this temp, when computer decides thats too much it grounds out a relay switch which hits power to the fan. The only thing that having the fans turn on doesnt explain is if the computer is getting the proper temp readings. If you can move the car right now, i'd try to make it to a auto shop and borrow the scanner again. see if a code threw since then. thats about all I know =/

 

How hot did you let it get ?

 

well they are set to turn on at 95 and 98 deg celcius and that works out to around 200-210 deg farenheit, and based on my temp guage, i let it get at least that hot.

 

Possible causes are: wiring, connections, bad fans, the tune, bad pcm(highly unlikely, you'd know if you have a bad pcm), relays, coolant temp sensors.

It should throw a code if at least one fan doesn't turn on. Coolant sensors could be read through a program on a computer via the data cable, like tts datamaster or freescan, and c.t.s.'s can also be measured by using a voltmeter. Shbox.com has information on reading coolant temp sensors.

 

Ok, i tested the sensors and the both read within a couple hundred ohms of each other. The a/c turns the fans on. i seem to be throwing a code but im not sure what because i dont have a scanner. can you count the blinks on a 94 pcm?

 

Nope, can't count blinks, its too bad, I like how you can on some stock thirdgens.

 

That sucks.

It looks like i was mistaken anyhow. I had both my coolant sensors unpluged when i did my ac test.


My pcm is throwing NO codes. and ac DOESNT turn my fans on. They come on when the diag connector has something pluged in it and no other time.

 

Well, one of my fans spontaneously started working today while driving. whatever lol if it works it works.

 

Well don't forget that the sensor for your guage is in a different spot than the one the PCM uses to turn on the fans.

Thats why I always use a scan tool when troubleshooting something like this. Unless you know what the PCM is reading, you're really going to be chasing your tail

-jason

 

I did shoebox's test to see if they were reading close to one another, they werent exactly the same but they were close.

 

Really look over the wiring. I'm trying to figure out why the fans would turn on when you plug in something to the diagnostic port, seems odd.

 

I had a very similar issue. It sounds like the fan relays and wiring are working fine. The problem appears to be that the PCM isn't making the decision to turn them on based on the input from the Engine Coolant Temperature Sensor. Check for continuity of the yellow wire from the ECT to where it enters the PCM. Then check the green wire from the ECM that signals the fan relays to turn on. I forget which pin it is, i'll look it up when I'm home if you can't find it. When the PCM is signalled by the ECT to turn the fans on, it does so by grounding that green wire which goes to the fan relays. Probe the wire when it leaves the PCM and see if it has continuity to ground. If it doesnt, try to reflash your tune (this is what happened to me and it worked).

 

Maybe if i clarify it will help. I wasnt sure if i could count blinks or not on the ses light, so i used the paperclip method, and that is when i discovered that the fans turn on with the 2 side by side pins shorted together.


That sounds like it could very well be the problem. Im 99% sure i wired everything correctly. Problem is if i have to have the tune reflashed i have to have it sent to me again.

 

The pin I was referring to is A11 on the LT1 PCM (at least for a 95 car) and it's dark green.... see if that gives a ground signal from the PCM when your temperature is up in the 220 degree range.

 

How do i do that when the plug is in the pcm? without striping the wire?

or do you mean test the ohms on the wire on the ect sensor itself?

 

I stripped the wire to do it. I first tested it where the green wire reaches the underhood fuse box and didn't get the ground signal... but before reflashing the tune, i wanted to be sure that the problem wasn't a break somewhere in the legth of the wire. I suppose you can test for ground when over 220 degrees where the green wire reaches the underhood fuse block and then test for continuity by removing the connector from the PCM and touching the A11 pin and the other end of the green wire in the underhood fuse box at the same time. That way you don't have to strip the wire. If you get no signal, touch that wire to ground and it should turn your fan on. I temporarily installed a manual switch until I could get it to my friend that has the tuning software