Help... Body Control Module???

WhiteTB

Original poster
Member
Nov 22, 2011
65
Okay so Ive been having some issues with the truck lately. Its in idle problem where the truck at idle doesn't feel right. My dash lights are flickering and my volt meter on the dash is moving form 14.5 to 14 volts. Also the tuck makes a sounds like it wants to die out at idle and only at idle. It has actually shut off twice in the past 2 weeks at a red light. I have been reading about this through the forums and checked for some solutions. I know my grounds are good so i know its not a loose connection. Next I'm going to clean out the throttle body even though I just did it this past July. And I'm not so sure this could be causing the problem but last year when I was doing a big audio install in the truck, when i was removing the rear seats somehow the seat bracket caught the ribbon on the Body Control Module and tore it a bit. I didn't really think anything of it because the truck ran like normal. But now I'm having this issue and I'm wondering if this could be the problem. Anyway I went a head and bought a used one on eBay. I actually found the same part number that's on mine right now. Now when I get it will it be just a plug in? I'm thinking I might have to get the pcm flashed to make it work right? Any help would be appreciated. Thanks guys
 

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RayVoy

Member
Nov 20, 2011
939
The BCM is not usually the problem when you are having engine troubles.

As the name implies, it operates the body electrics.

Usually, an engine problem is caused by a fuel/air/spark problem. The PCM is the computer that oversees the proper application of the fuel/air/spark.

The PCM tries to adjust/compensate for any problems with the f/a/s.

If there is an idle problem, the problem is probably under the hood.


Getting back to the BCM, it looks like you have a broken circuit, but if it has not caused any problems in the time since you broke it, it is probably a circuit that you are not using, or something that is duplicated (like a ground)
 

WhiteTB

Original poster
Member
Nov 22, 2011
65
RayVoy said:
The BCM is not usually the problem when you are having engine troubles.

As the name implies, it operates the body electrics.

Usually, an engine problem is caused by a fuel/air/spark problem. The PCM is the computer that oversees the proper application of the fuel/air/spark.

The PCM tries to adjust/compensate for any problems with the f/a/s.

If there is an idle problem, the problem is probably under the hood.


Getting back to the BCM, it looks like you have a broken circuit, but if it has not caused any problems in the time since you broke it, it is probably a circuit that you are not using, or something that is duplicated (like a ground)

Yea I figured it probably wasn't the issue since this happened a while ago with no issues. Either way I want to replace it so I bought one.
Back to the issue. Ill clean out the tb again and see if that helps. Then Ill check the plugs. Ill see if that helps
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,192
Brighton, CO
Diferent Engine, but I had a simalar problem.. Turned out to be a bad battery.. Had it tested multible times, and always tested good. All of a sudden, at random, my battery went dead, and I replaced it. have not had a idle problem since.

My volt guage was also doing the jumping around on the needle.

EDIT: I beleive the data strip that is torn is replaceable by itself. It should be able to be disconnected at both ends without issue. This would prevent the possibility of haveing to get your BCM reprogrammed.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I agree. The flexible circuit unit isn't part of the BCM. If you bought a new BCM, did it comes with a new flex? Odd.

Reports are that new and almost ALL used ones have to be reprogrammed at the dealer unless your option list matches exactly the donor vehicle. Evil GM design to make sure you come back once in a while and remain addicted to them.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I would go somewhere and get the battery tested as well. Mine did funny things as the battery died. When they tested it I was just a couple hundred amps below rating, but it was screwing with the idle and then throwing random codes. The battery cleared up everything.
 

WhiteTB

Original poster
Member
Nov 22, 2011
65
the roadie said:
I agree. The flexible circuit unit isn't part of the BCM. If you bought a new BCM, did it comes with a new flex? Odd.

Reports are that new and almost ALL used ones have to be reprogrammed at the dealer unless your option list matches exactly the donor vehicle. Evil GM design to make sure you come back once in a while and remain addicted to them.
I bought a used one on ebay with the same part number. Looks like it comes with it from the picture. Ill find out Friday when it gets here. I figured that it would have to get re-programed. Can I just switch out the ribbon on them?
HARDTRAILZ said:
I would go somewhere and get the battery tested as well. Mine did funny things as the battery died. When they tested it I was just a couple hundred amps below rating, but it was screwing with the idle and then throwing random codes. The battery cleared up everything.
Battery is basically brand new I bout it last month and its a very good battery XS POWER D3400

I bought new spark plugs and some throttle body cleaner. I will check back Friday when I have time to work on the truck
 

WhiteTB

Original poster
Member
Nov 22, 2011
65
the roadie said:
Ribbons are all the same. Swap away. Be careful.

Sweet. That would mean I wouldn't have to get the bcm reprogramed right. Id just be swapping out the ribbons
Roadie to the rescue again
 

Mark20

Member
Dec 6, 2011
1,630
I'd disconnect the battery while swapping incase any of the leads in the ribbon carry power.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,192
Brighton, CO
WhiteTB said:
Sweet. That would mean I wouldn't have to get the bcm reprogramed right. Id just be swapping out the ribbons
Roadie to the rescue again

Now I dont mean to say anything, but I beleive it was me that suggested to swap out the ribbons.. :biggrin::yes:
 

WhiteTB

Original poster
Member
Nov 22, 2011
65
Well I got everything done today. Swapped out the ribbon with no issues. Changed out plugs, cleaned throttle body, changed out belt tension and belt as well. I am still getting the same issue at idle. Seems like something is wrong with the belt or something in that matter. The belt seems to have to much give and doesn't seem tight enough. Think that's why im getting this issue at idle. Only reason I can think of is with my 300 amp alt they used a smaller pulley. Maybe I need a smaller belt?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
WhiteTB said:
Only reason I can think of is with my 300 amp alt they used a smaller pulley.
Wish you had thought this was relevant enough to share earlier.
Maybe I need a smaller belt?
Who specified and installed the alternator? If it was a shop, they should have done the math and selected a smaller belt.

That said, jumping voltage from a slipping belt shouldn't affect idle RPM. Assume you disconnected the battery during the throttle body cleaning to force a relearn. Have you driven it enough to actually go through the relearn process? Does the drooping idle go away if you force the AC compressor off with the snowflake symbol?
 

WhiteTB

Original poster
Member
Nov 22, 2011
65
the roadie said:
Wish you had thought this was relevant enough to share earlier. Who specified and installed the alternator? If it was a shop, they should have done the math and selected a smaller belt.
Sorry I forgot to mention that. And the alt was installed by me and one of my teammates.

That said, jumping voltage from a slipping belt shouldn't affect idle RPM. Assume you disconnected the battery during the throttle body cleaning to force a relearn. Have you driven it enough to actually go through the relearn process? Does the drooping idle go away if you force the AC compressor off with the snowflake symbol?
The rpms don't jump really i see it at 650 maybe 7. I did disconnect the battery and removed the fuses for the pcm for about 30min I also drove about 8 miles after. I am seeing an improvement in mpg which is great. But this idle issue Is bothering me, I'm trying to figure it out before I take it to the mechanic. I made a video of what is going on. Looks like the belt tensioner, but that belt tensioner was replaced 2 days ago and is doing the same thing as the old one. Also new belt on it as well. Please help

[video=youtube;QBj0WZ4OnA8]http://www.youtube.com/watch?v=QBj0WZ4OnA8[/video]
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,192
Brighton, CO
It looks like you are going to need at least a 1/2 inch smaller belt to acomadate the smaller pulley..

However, we still shouldnt see the volts moving like that. Listening to the engine, it sounds like the truck is idle hunting. CPAS maybe? Throttle body dirty? Someone more familiar with the I6 engine will have to responde with more info.
 

phanpride

Member
Mar 10, 2012
16
Not sure if it is relevant but my voltmeter does the same thing, but only it was because I installed HID's
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,192
Brighton, CO
My Volt guage was also doing that, and it was due to a bad battery, and alternator. But he looks to have some pretty high end stuff.. So I dont know if its that. unless his internal voltage regulator is about to shoot craps..
 

neelskit

Member
Dec 7, 2011
69
Remove the belt and see is the idle fluctuates. This will eliminate either the engine or the belt drive as the cause of the problem. I'm leaning towards your alternator as the cause of the problem... Do you still have your stock alternator to test with?
 

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