How to test the BCM

[pappyl]

1995 SSEi

Fan is working only on Hi. Climate control "looks" like it is working...

I went to the boneyard and pulled (no joke) 8 BCMs. Stuck each in and raised/lowered the fan speed. NONE WORKED.
(Yes the big one - with the aluminim cooling fins)

Is there a way to test a BCM when it's out - using a mutli-meter say?

I've spent a small fortune getting the AC working, I'd like my climate control to work right...

I'm worried it may be something else - like the actual climate control module..


Any ideas are welcome...


Thanks

[mntnbkr]

I assume you're talking about the blower fan for the heat and A/c as opposed to the cooling fan for the engine / radiator.

If you're blower motor only works on high, then there could be a couple different causes, but most likely, your BCM is not the problem.

I'm not terribly familiar with the A/C system in these vehicles yet, but I know there is a climate control module that can go bad, and there is also a resistor pack for the blower motor that can go bad. Typically when resistor packs go bad, you start loosing fan speeds until only the high speed will work.

I can't give you exact instruction since I don't have my FSM with me right now, but if you want to check the resistor pack, you have to access it from under the hood. It's located under the passenger side windshield wiper, and you have to remove the cover for the maxi-fuse relay center.

One of the gearheads will surely be able to help you pinpoint the problem a little better than I can...and help you solve it too.

Reference:
viewtopic.php?f=45&t=2432&p=22865&hilit ... ack#p22865

viewtopic.php?f=19&t=9235&p=99487&hilit ... ack#p99487

[swampthing]

the resistor is bad 99% sure, thats what most vehicles do when it goes.

the blower fan has only one speed which is what you are getting when you turn on high, in order to have lower speeds there is a resistor pack that has however many resistors in it for the desired speed so that the fan is actually getting less power to it.

i have not had this problem on my bonneville, but i did have it go out on my truck, relatively easy fix and it shouldn't be an expensive part

[imidazol97]

Someone already suggested checking the resistor block. Follow the leads from the motor to the top of the blower channel that the blower motor sits in. The relay center has a couple of screws holding it in place and those out it can be moved up a little to make room to work.

I believe also there's a relay in the circuit for the low speeds and a relay for the high speeds. I may be wrong on that, but I believe on the manual speed control systems that's the way it's set up.

[pappyl]

Guys,

Maybe terminlogy here, I think I'm missing something...

There is no resistor pack - there is a Blower Control module - as I have a climate control system.
That is located just above the blower fan - in the housing. Need to pull the relay/fuse centre back to extract.

I removed 8 of those from junkyard vehicles and tried them. None worked - no low speed on blower.

see #7 on viewtopic.php?f=19&t=9235&p=99487&hilit=resistor+pack#p99487

The link to the diagram you provided actually calls it a BCM.


So, that is what I'd like to pull out and test - if there is a test for it.

[RegencyRoyale]

Yes, you have a BCM (Blower Control Module) if you have Digital Electronic Climate Control. It looks like this:

http://ecx.images-amazon.com/images/I/4 ... SL500_.jpg

I'm unaware of any way to test though, but it does seem strange that 8 of them would be dead and dead in such a way to cause the same problem as your original...working on HIGH only. I don't think they alwasy fail in that same way. Mine didn't. It just stopped working in all speeds. Out of 8 you would think there would be at least one that worked differently, either not run at all or worked intermitely...About the only way to be sure it is the BCM is if you knew someone who had a car with the same setup and you could swap in a known good BCM and see if you have the same result as with the other 8 (9 including your original)...

[pappyl]

Yes - that would be nice.

This all started after the fuse blew in the passenger side - for the A/C.
The garage that was charging my A/C actually brought it to a GM dealership to fix. The dumbass mechanic said that I needed a new computer. He couldn't hookup to the HVAC because it was dead. Incompetence.
I crawled around underneath and found the blown fuse and replaced it.
After that, the fan only worked on high - but my AC works just fine. Why did it blow? - dunno.

This is ridiculous. I'd like to kick some GM engineer's ass.

I've gone through 100 different posts on how this HVAC system has failed - 100 different ways - bad actuators, faulty modules, melted vacuum lines and failed programmers. People no heat in the winter, units failing after their battery dies.

What a bunch of *shoot*.

Ironically I'm a tried and true Chevy man - everything I own is GM.

[mntnbkr]

Sorry for the hasty and non-precise reply previously. When I saw you mention BCM, my brain immediately thought "Body Control Module" (from newer cars). Blower Control Module...OK. So, you changed the Blower Control Module (resistor pack) out 8 times and it didn't make a difference? I think its safe to rule out the resistor pack as the source of your troubles.

I'll have to think on this some more before I can provide any useful information. Hopefully in the mean time, one of the gearheads will stop in and solve all of your troubles.

[00Beast]

Find another ECC unit at the JY and see if it fixes your problem.

[ddalder]

It sounds like you've done a lot of research. I would like to offer some help, but I personally have no experience with your vintage vehicle. Regardless, there is a lot of knowledge amongst members here. Please don't get discouraged by some of the less than helpful remarks (I for one believe you're trying to "deal with it"). I'm sure someone will chime in with some additional information Stick with it! I love some of the older cars.

[gmman]

i have had similar experience working on my 96 Bonn SE ECC. my failure mode was blower motor failed to shut off when ignition off. had to pull fuse in relay center to stop blower when car not in use. problem was in ECC computer (called program control module-PCM-in 96 FSM). i checked dealer price for PCM-$800 and old unit not repairable or exchangeable. they did however give me the new part number for the PCM. old part number is 16201492. new number is 16258362. assuming that your trouble is in the PCM, you might get lucky as i was to find the new PN in a JY. only cost me about $50.

i agree with previous post that it is unlikely that 8 different BCMs would give you the exact same sympton as original if problem was in BCM. seems to add credence that the problem is in PCM.

as a further check if you have not already done so, verify that air flow changes to different vents as you change vent mode selection. if air only comes out defrost and floor vents this would further point to PCM.

to my knowledge there is no documented procedure for testing the BCM out of car. as in previous post, the manual HVAC system depends upon selecting various resistors in series with blower motor. best i can tell from reading 96 FSM, the BCM output to the blower motor is controlled by a series of pulses with different widths (called pulse width modulation) and width determines blower motor speed (as i tried to depict in drawing). basically the BCM acts like a continuously variable resistor.

seems i remember reading a post from a BC member quite a while ago that said he could manufacture a BCM perhaps on the chassis of an old one. if he is still online, maybe he will add to the understanding.

[RegencyRoyale]

...Post Deleted...

[Jrs3800]

The Blower Control Module in these cars fails.. Its very common..

Chances are the BCM is either dead and the blower motor does not run no matter what you have selected on the ECC... Of the Blower will be stuck on high speed... That would be the 2 classic signs of a failure.. But you should test the blower motor to make sure its not dead..

As for the ECC head, its very rare for them to fail... That goes from 87-99

[Mechanical Mike]

PM me with an email address if you want me to send you a wiring diagram.

[pappyl]

Sorry for not getting back to you guys sooner - been a busy weekend...

A few things I can clarify - hopefully provide some clues...

1. The blower motor was recently replaced. Bearing on the old ones were going. Wife got tired of hitting it with a snowbrush - lol. New blower was on when this problem "started".

2. The blower speed is on high - maybe not as high as possible - but high and changing the speed on the climate control panel makes no difference at all.

3. ALL other functions work properly. This includes the actuator on the plenum - floor, mid,defrost and recirc all work properly, get heat and cold as requested.

4. I tried to find a climate control panel at the junkyard. No luck so far - and they want a pretty penny for'em if I do locate one. It's my logical suspect, given I've tried so many of the BCMs - you wouldn't think they're all bad...

5. Given the BCM is a digital variable resistor based on variable voltage output from the fan speed control - not sure how I could test it with a multimeter. BUT, maybe I could test the DC voltage going IN to the controller from the climate control module?
Lower the fan speed, voltage either raises or lowers...?
Question is - which wire...

mechanical mike - I'll try to PM you tomorrow. Appreciate your offer.

One thing to note...
Wife had bought a bottle of some liquid fragrance stuff - was in the glove box. Found it had leaked. I surmised it could have caused the original short of the AC system. (The AC fuse on the passenger side)
I was under there recently - there are quite a few electronic boxes under there - I know not what they are... could this be related to a cause? Some other relay maybe... Dunno.

[1fatcat]

5. Given the BCM is a digital variable resistor based on variable voltage output from the fan speed control - not sure how I could test it with a multimeter. BUT, maybe I could test the DC voltage going IN to the controller from the climate control module?
Lower the fan speed, voltage either raises or lowers...?
Question is - which wire...

Should be a gray wire with a white stripe. Red is power, black is ground and purple is power output (to blower motor).

[gmman]

the way your ECC is operating is blowing my mind. it would appear that the ECC head (brains of the system) is performing normally but that would have to mean you found 8 BCMs in an identical failure mode to your original. and that seems to mean that your original BCM is good and that you found 8 good BCMs in the JY. assuming that is true, then there is one other possibility. there is a 10 amp fuse on the passenger side kick panel which is in a feedback circuit from BCM output back to ECC head. if that fuse is blown, the ECC head would always think that there was not enough voltage going to the blower motor and keep calling for max output from the BCM and therefore hi speed fan operation. i remember you said you have replaced a fuse but i am not sure which one. if it happened to be the one in question, recheck to make sure it did not blow again. if blown, replace making sure that is correct amperage.

as a desperate measure, i will mail you a known "bad" BCM whose failure mode is no fan operation. let me know if you think that would help.

i doubt you will be able to tell anything using a voltmeter to measure BCM input from ECC head. i tried with no conclusive results. i think you would have to use an oscilloscope to witness that pulses are arriving at the BCM and that they vary in width as you call for different fan speeds from the dash panel.

[pappyl]

gmman,

Thanks for the feedback - I was thinking AFTER I posted my last comments - based on what you posted - that was the case - I'd need a scope to see the pulses.

So - there may be another fuse involved here. I'll look for that feedback circuit fuse. I remember checking all the fuses last time - but I could have missed one.

What I'd like to do is find someone who actually has a working system and swap a couple parts to find the problem - just not had any luck there - yet.

I don't think the non-working BCM would help localize the root cause. I need to prove the BCM is working.

I'll check tonight.

If I remember right - there are more that few electronic modules under there (to my surprise). How many cars have 2 fuse panels?

Thanks

[1fatcat]

Two or more fuse panels re not un-common. Many vehicles have three.

[gmman]

the blower motor feedback fuse is designated F11 in 96 FSM. i don't remember if it is labeled as such in relay center.