2002 L100 0481 Error code

[retsamidej]

Greetings! I have a bit of an ongoing problem, and I'll try to keep it short but thorough. I had been wanting to install some manual fan switches for my car for a while. It's kind of a OCD thing that I like to shut down the car after the engine cools to around 1/4 - 1/2 on the temp gauge. I'm usually found in the driveway after getting home sitting and waiting, turning on the heater, ect. I had found a forum that described an owner with a 98 model making switches and connecting them to the relay in the fuse box. Wonderful! so i immediatly set to work to fashion my own.

youtube.com/watch?v=USlQzpenajE

Did a good job too. This is where the sh$% hit the radiator fan. I looked in the box and gosh, they decided to move the relays to their own box on the battery. Opening it up I find not only does it have its own board, but 5 relays. Joy. So, knowing not to start shorting things out, I whipped out my digital voltage meter to trace which relay did what. Of course my hand slipped shorting things out. from then on, there didnt seem to be and power going to the big 2 way relay (the 30 87 86 one). Now the check engine light is on with error code 0481 which is the coolant fan 2 circuit. It seems that I've lost my low fan speed, and from what I can hear I only have medium or high. not being able to do much, i soldered the manual fan switch to the only relay that I felt safe using. The switch would up the speed of whatever setting the fan was on at that time. If the fans were on high I would flip it on while passing people on the sidewalk and they would stare because it sounded like aircraft landing gear.
I'v also noticed that both fans turn on and the same time when their on, and run at the same speed. Not sure if they are supposed to work individually or not. Also, they appear to both be running off of the Fan 1 fuse, as removing the Fan 2 fuse does nothing.
This weekend I removed the 5 transistors that are on the board as I though those would have been the first thing to go. They are completely fine. I've checked the relays as well. No problems. I'm pretty puzzled on this one.

I had a problem with the car a few months back where the dome light came on when it wanted to. It wouldn't flicker, it would either be on or it wouldn't. very annoying when getting in at night. I managed to fix that after tearing the car apart. I didnt find the actual problem, but I'm sure it was something INSIDE of the drivers side cabin fusebox. Not wanting to break into it, I made a jumper from a working orange wire to the non functioning one right next to it. There is no fuse for that circuit, and it controls the dome light, glove box light, and trunk light. A bit off topic but hopefully this helps someone because I couldn't find any help about it.

The car is functioning fine in that its not overheating, it just turns the fans on high a little while after it should have turned the low on, both fans are running off Fan 1 fuse, and their both on at the same time. I appreciate any help I can get. I don't like that check engine light on, and thats bad if something does happen. I checked it today and found a secondary air injection failure? hopefully its just a fluke. Thanks again.

[fdryer]

Welcome to Saturnfans!

Well, you seem enamored of our three speed fan circuitry so here are the wiring diagrams to examine. This fan control module (FCM) is controlled by the pcm to select fan speed appropriate to various factors.

You'll find more info searching past threads about fcm's and how they work.

[retsamidej]

Thanks much! Don't know when I'll get to it. Sometime this week with the amount of homework I have. Now after I get this situation fixed I plan on leaving this box alone and just making my own board with two relays so I can continue with my idea. Since I have two switches I want to have one for fan one and one for fan 2. Im going to include two 30 amp fuses in this board and hook it from the battery into this board and splice it into the fans directly. Are there any problems you can foresee in doing this? Much obliged for the help and any additional feedback is very welcome. A little loopy right now from all the work so to bed I'll go

[fdryer]

Whether you're studying to be an electrical engineer or simply putzing around, our fan control modules are designed to work the way you're imagining, and then some. As I mentioned before, search for the fcm technical description, it'll be in italics to emphasize reprinting from the service manual. All three speeds are done automatically without any switching needed from drivers too busy attempting to text/dial the radio/navigate a GPS screen/conversate with car pool friends/finger other drivers/whatever.

How do you know the fcm is faulty? Did you try to test the low speed fan directly off the battery? While fcm's do fail, its usually easier to troubleshoot fans, wiring, fuses, and relays before tearing apart the fcm. Some get away with a couple of raps on the fcm to free possible stuck relays within. Other than finding cold solder joints (very rare) the fcm is trouble free.

If you insist on bypassing the fcm functions, be sure where to splice in your modifications to take advantage and not cause more issues with circuit interference...............................

[retsamidej]

Well as stated somewhere above I unfortunately happened to short something out while testing for points on the board. After that there seemed to be power failure in one side of the board so I was assuming it was this board to be the problem.

[fdryer]

Try ebay for used fcm's. There seems to be some difficulty from members trying GM. Although not a stocked part at every GM dealer, GM parts online may be a source.

[retsamidej]

I was thinking of that but thats when I pulled the board and checked everything on it that could go wrong and I haven't found anything. Their really arent that many components on the board, not to mention ones that could go bad. The 5 relays are good, the 5 transistors are also good, the diodes are good. The resistors are also looking good but i haven't checked each to their specifications. I'm thinking its either that or something else. I did notice two lighter gauge wires going into the box, probably from the ecm. hopefully its not that, though I heard elsewhere that the ecm either works or the car doesn't start. Thanks for the quick replies. I'll be leaving for the rest of the day soon so any more info you need till then will be gladly provided.

[retsamidej]

Managed to get a secondary board made. Don't mind that relay in the center, It's for a pair of long horns.

[retsamidej]

A little more info i have found out: only throws the code when ac is on, upon deleting the code while engine and ac running the fans seem to go back to normal (at least the ac air is still cold) but the error comes back after about 10 seconds so im not sur

[retsamidej]

so upon looking more into the problem i remember where i shorted the fcm at. it was the little blue wire coming out of the fcm. when your in front of the car looking towards the back of the car, its the 3rd wire from the left on the left connector. I assume since this is going to nowhere but a relay that this is the problem, and also since this is the wire that was shorted. i managed to trace it back to the fusebox, but all of the fuses are good. I even opened the fuse box (with the battery disconnected) and found the wire connecting to a pin towards the middle of the box (not much help i know) but i havent found anything on top that connects to that.

This problem is really frustrating and between school and homework its really hard for me to determine what the cause could be. Im guessing since it controls the relay that whatever that control is might be shot but i dunno. please help

[fdryer]

Did you study those two wiring diagrams in post #2?

[retsamidej]

I have been studying them. Sorry it's taken so long to get back. I haven't had time to do much on it but study the diagrams. I've narrowed it down to either the fuse box or the pcm. Do you have any schematics of the pin layouts of either of these? Thanks. Once school lets out I'll be able to get all this in order.