Ok, so i've been working on this for like 2 months now. Let me start at the begining, The fuse to my cooling fans blew. So i replaced it. And that one blew immediatley. So to check the fans i unplugged them both and put a new fuse in and it blew. I don't even have to start the car, just turn it to on, and it will blow the fuse everytime. Ok so there must be a short somewhere between the fans and the fuse box right? so i trace wires and trace wires and then i trace wires some more. And no bare wires, no burnt marks, no chaffing. Now i'm starting to get upset. . I really really want to drive my car again. Does anyone have any ideas? Could a bad temp sensor do that? or some other sensor or bad part? Oh yea, i also checked all 3 relays that go to the fans and they were all good. By the way my car is a 1996 Z28 A4 with 85,000 miles on it wich also makes me even angrier that it is doing this. Please someone help.

 

According to the schematics on Shoeboxe's site, the fan fuse protects the control circuit for the relays. There is a fuseable link(Wire that burns apart) that protects the fans.
http://shbox.com/1/fan_schematic_1995.jpg

You're looking at a short to ground between the fuse, relays and computer. Grab an Ohm meter. Do all your testing with the key off. Pull the fuse and put one of the test leads into the side that doesn't have any power, that's the side that goes to the fan relays. Then pull all three fan relays out. Touch the other test lead to the Neg. Bat. terminal or a good ground point. The meter shoudn't do anything. That means the brown wire is insulated from any ground. If the meter shows low resistance, you have a problem in that brown section of wire. If it tests good, you have two wires that go to the ECM that control the fans, A10 & A11. Move one of your test leads to Dark Green wire to relay #1. Check for short to ground. If it tests good, check the Dark Blue at both relays #2&3. If there's a short circiut indicated, disconnect the ECM. If the short goes away, the porblem is the ECM.

 

Thanks for the info. I tried that once but not as in depth as u instructed. I will try that first thing tommorow. I'll let ya know what i find out. I appreciatte the help. Thanks

 

The A/P-fan fuse also powers the AIR pump relay. Unplug your AIR pump relay and see if the fuse blows.

 

dosent it also power up the o2 sensors?

my fan fuse keept blowing and it was an o2 sensor wire scraping on the ground and shorting out

 

Not on a 1996...

 

gotcha

 

I checked the AIR relay and it was good, Just to be safe let me make sure i'm checkin these right. I just take the relay out, hook 2 wires to a 9 volt battery, and touch the 2 wires to the 2 prongs on the relay. And if i can hear it click over i assume its good. I'm runnin to get another box of fuses now so i can try just takin it out and seein if it blows. Also gotta stop and get the ohm meter back so i can do that 2 day to.

 

Ok heres what i got so far. Checked the AIR relay and it was good. Took a test light and checked the fuse. current on one side, nothing on the other. Checked the fan relay 1, current on one prong and no others, Checked fan relay 2, current on one prong and no others, Checked fan relay 3 and no current on any prongs.

 

Sorry, got a little ahead of myself. So now i need to disconnect the ecm right? I checked the green wire on relay 1 and the blue on relay 2 and 3 and there was no current on them. I also ran a code scanner on it and it gave me p1641 and p1642 wich says fan control relay 1 and the other is fan control relay 2 and 3.

 

With the relays out and the fuse out, you have power on one wire. That's correct so far, because you are getting power through the fuseable link that actually powers the fans.

A relay is like a remote switch. They are useing small gauge wires and lower current to operate the relay"click sound". That click only means it clicks. There are contacts inside that press together and make a connection. One side is the power wire from the fuseable link. The other side will be the wires going to the fan motors. That wire is considerably heavier and to keep from running heavy wires all over the engineers use a relay out near the fan motor and the power source. Then they run small wires to control everything.

I don't see any results from the Ohm meter test from the fuse side that doesn't have any power to the relay trigger wires, and a test of the wires going to the computer. If you have a grounded wire, it's a short circuit that is blowing the fuse.

You have to look at it like two seperate systems. The control side is the one that's blowing the fuse. The business end is the side that actually runs the fan motors. If you want to manullay trigger the fan motors to see them run, make a jumper wire. Plug one end into the relay plug that has power(Fuseable link) and the other end to the wire going to the fan motor. These will be the opposite terminals that you are triggering the relay with that make the clicking sound. Your fan should run. Again, your short circuit is on the lower power control side. I hope this makes sense.

 

Ok its took me awhile, Havn't been home much latley, anyway i unhooked the ECM and the fuse Did NOT blow. Ok so do I need a new ECM or does that just mean that the short is in the wires coming from the ECM?

 

To answer that question you need to connect your Ohm meter to the pins, A10 and A11 in the harness to the computer and to battery Neg. post. You shouldn't have any connection. If you get any reading, the wire has a short to ground somewhere and that's what you have to track down. Or, you can run a new wire from point to point and connect it up.

If these wires check out good, no short to ground, I sounds like there's no other explaination other than the ECM has an internal short. If that's the case, you could wire up a fan bypass switch and not use the computers to run the fans.

 

Ok This seemed wierd to me, I checked A10 and it had voltage and u could hear the relay clicking on. I checked A11 and it had voltage and also the fans come on while i do it to. Is it supposed to do that?

 

That means your triggering the relays with the meter when you provide a ground. I didn't think of that, but that's what the computer does to control the fans. If the fans run and you're not blowing a fuse, then it's looking like the PCM has a short in the fan circuit.

You can rerun the test by first pulling the fan fuse. Then nothing will activate and you can get an OHM(resistance reading). You were able to read voltage on those wires because they are wired directly to the battery through the fuse.