GMLAN and aftermarket radio. Compatability issues??

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#1
I have gotten mixed reports regarding removing the base stock GM radio and replacing it with a aftermarket radio. Anywhere from the airbag NOT deploying in a crash to the car not passing the NYS emission inspection. No, I'm not making this up.

The radio is only the base model. with NO "Preference" controls. It can't even change the level of the 'chime'. With this class 2 data bus, where everything is tied into the LAN system, this has me worried with all these stories I have heard from local stores that sell radios.

Since this unit has no data functions other than being tied into the data bus for radio related issues (DTCs') and the 'chime' feature (which I could live without), if I don't go with one of those overpriced ($80-$100) adapter cable assemblies with the chime interface, is there any problem with this??

My car is a Chevy 05 Classic (fleet version of the Malibu).
 

sunny

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#2
Do not cut the original factory wires!! Spring for the adapter cable because it's MUCH cheaper than messing up the factory wiring system. There's no telling what all will be effected and what will be messed up without them. You could probably find the needed cable at Crutchfeild or any good retail supplier of car stereo. In fact I have always gotten my adapters free or discounted when getting the new stereo from Crutchfeild.
So I'm wondering if your going for a full tilt system with multi amp setup, components in the doors and 12" subwoofers or what? I love installing those big systems. :)
 
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#3
I already have the radio. It was pulled from my old car. All I plan on doing is replacing the four speakers and using the Pioneer radio I already have. That's it. Nothing fancy. That adapter from Crutchfield is $80. I can'r see spending $80 for chimes I could car less about if that is the only downside. I have no intention of "cutting" anything, hence the reason for the wiring harness.

I have the Helm factory manual and there is only one data bus connection to the radio. The SM states the radio will send DTCs' back to the BCM if there are problems with the radio. It will set a DTC if the radio isn't there. I can't see the missing 'chimes' would fail a emission test. ???

I'm assuming these reports are from 'bad' installs.
 

jjm

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#4
Baloney!

Amazing how these myths are propagated. Unless you directly wire something into the Class II bus that shouldn't be there - effectively shutting down Class II communications - removing the radio won't affect the airbags, emissions, or anything else... sheeeeez!

At worst, you won't have any chimes and OnStar (if equipped) will no longer work since the VIU/VCIM will no longer communicate with the IRC. The worst thing that's gonna happen is you'll set one or two codes, U1128 (Loss of Communications with IRC) and if the radio has an amp, U1129 (Loss of Communications with AMP). If the vehicle had a radio "delete" option, depending on the vehicle, that parameter can be set via the Tech2 so the IRC is not searched over the bus.

Sounds like classic fear mongering we've heard about with almost every new automotive technology that has ever been. I'm old enough to remember the scary stories about electronic ignition systems that would leave you stranded, and how electronic fuel injection systems were "unfixable".

Look at it this way... let's say you have a home network and one of the computers is used only for listening to MP3's. If you take that computer out, does the other machine you run Quicken on lose all your household finances? What about the machine you run home automation on, do your lights go out? Pretty much the same thing with the GM Class II bus.

Joe

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#5
This is the first intelligent answer I have heard since I started looking into this. This is my first GM product. This replaced a '89 Dodge Spirit that I loved (rust and a unobtainable part did it in). I have spent a week reading the SM and this data bus that has almost everything connected to it seems to make the car more of a challenge to work on electrically then it is mechanically.

The 'air bag' story was from Circuit City and they claimed someone had a radio installed w/o the fancy adapter, the car was in a crash and the air bag didn't deploy. The next story was another car didn't pass the NYS emission inspection because the correct adapter wasn't installed. Still another story was a low oil pressure/level light or gauge didn't show the low level/pressure and the engine seized (or something as this).

The only connection I could find in the Helm manual was a DTC is set if the BCM doesn't see the radio (that U1128 you mentioned). Ok, what does that have to do with air bags, oil pressure indicators or inspection? ::)

BTW, no OnStar or separate amp. You used a couple of terms the manual didn't; "VIU/VCIM" & IRC. What are they?
 
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#6
The only thing I could think of is if the data bus wasn't terminated (no radio), would that cause a issue? The other thing would be if that data bus was 'zapped' and damaged either the BCM ot PCM.
 

sunny

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#7
I guess I should have explained a bit better. You are far better off using the adapter than cutting the factory wires and trying to figure out what wires to use. If you are wiring the stereo up as a "stand alone" unit then there should be no problem unless like jjm said by not having the unit there. As a stand alone unit I mean go with all new power and ground wires then run new speaker wires instead of patching into the factory wires you won't cause any problems.
I had an S-10 came to me once that the boy had cut his wiring for the radio and then didn't have dash illunination cause it shared some of the cicuitry with the stereo. I rewired the plugin and wired the stereo all by itself with the plug just laying there and all was good. Those big chain stores don't always hire the brightest people and they try to sell you anything they can. Stick with well known reputable stereo shops.
 

jjm

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#8
Intelligent answers - that's what we're all about here!

The reason I don't buy any of those stories was because if a radio was installed incorrectly, wouldn't the airbag light come on immediately afterwards? Besides, even properly functioning air bag systems don't always deploy in a collision - they're not supposed to! Emissions failure... check engine light never came on (which it would if something was done wrong)? And the oil pressure story... we'll that one just took the cake... if the radio causes the gauge or light to go out, wouldn't you manually check the oil then? Besides, what are the chances of someone running the engine dry between oil changes? Most vehicles cosume what... a quart every several thousand miles? So unless you abuse your engine to begin with 10,000 or 20,000 mile oil change intervals, that oil story wreaks of BS.

VIU and VCIM stands for "Vehicle Interface Unit" and "Vehicle Communications Interface Unit", respectively, are the OnStar control module - VIU is the module code a Tech2 will see. IRC (also the module code the Tech2 sees) stands for "Integrated Radio Chassis" - which you guessed it - is the radio. So for example, if you pressed one of the OnStar buttons, the VIU/VCIM would command the IRC over the Class II data bus to mute the radio.

Sunny gave you some good advice on wiring which I neglected to mention... leave the factory harness alone (don't cut anything) unless you use that adapter, or wire the unit up "stand alone" with its own separate power, grounds, speaker runs, etc. And he sure is right about the big chain personnel.

Joe

P.S. I've been there with rust and lack of parts doing an otherwise good vehicle in!

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#9
if a radio was installed incorrectly, wouldn't the airbag light come on immediately afterwards?
If it affected the SIR function, but why should it in the first place?
You are far better off using the adapter than cutting the factory wires
I never planed on 'cutting' anything. I planned to get just a straight wiring harness as I did with the Dodge. Solder one wire at a time from the GM jack to the Pioneer plug. Then just plug the 'intermediate harness' into the existing GM jack. When I sell/trade the car, the old radio goes back where it was (if I want).
As far as running new wires for the speakers, isn't that overkill? They are already there and decicated to just the speakers, so I can't see any issue here.
Those big chain stores don't always hire the brightest people and they try to sell you anything they can.
CC fired all of them., They were making to much $.  ;)

I can see why I didn't see the terms VIU & VCIM since those are OnStar terms that I don't have, nor want (thank goodness).
 
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#10
Any more insight on GMs' LAN system and the radio? Will a non terminated databus cause a issue other than it reporting that device not responding or missing?
 

jjm

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#11
Not much more to tell... it's a relatively simple system.

And yes, you can leave device(s) disconnected without any problems (other than affected devices) other than a code being set. There shouldn't be any "termination" issues... you sound like a computer guy, so this isn't like a SCSI bus that needs proper termination; think of it like a USB bus where multiple ports can be left open.

Joe

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#12
it's a relatively simple system
Not according to the SM and all the stories I have heard. Everything seems to be tied together and it appears DTCs' are plentyful.  :eek:
you sound like a computer guy, so this isn't like a SCSI bus that needs proper termination; think of it like a USB bus where multiple ports can be left open.
Electronics guy. Understood about being similar to USB ports. I'm really surprised there aren't more posts on this issue.
 

sunny

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#13
You have to understand that most mechanics will caution you about installing an aftermarket stereo for good reason. Anyone that has worked in a repair shop for more than a year has seen more than their fair share of electrical nightmares from people installing aftermarket goodies such as remote starters, stereos, burglar alarms and video or navagation systems just to name a few. I even had a Chevy truck with multiple electrical problems and a smoked VCM just from an added camper shell with optional lighting on it. It was wired into a VCM circuit for power because the guy found the first wire that had power with the key on. And the newer the car is the more things are tied into VCMs and various modules.

That is why I highly recomend the use of adapters or stand alone wiring for any aftermarket install no matter how expensive the adapter is nor how simple the wiring seems to be such as speaker leads. An electrical designer/engineer has already figured out what circuits you need and can use to get good results from your addition. I still highly recomend forking out the $80 dollars to avoid a major electrical malfunction. It could end up costing you ten times what you are trying to save. Every mechanic at this site has seen it too many times. But it's still up to you to make the final decision. Good Luck!
 
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#14
I completely understand this. The safe course is the best course. One thing I will pratially disagree with you on is this;
An electrical designer/engineer has already figured out what circuits you need and can use to get good results from your addition.
........after the marketing depatment of that 'add-on' company saw a revenue source.  ;)

Take into account, since this was a 'fleet' vehicle, there is NO OnStar, NO extrenal amp, NO preference control through the radio (it can't even change the chime level by holding the #6 preset down whilre the radio is off), it isn't a Bose system, there is no trip log feature(s) and there is no powered antenna. This is as stock of a radio GM seems to offer without any of the BS add-ons. I would be tieing into the wireness harness that was meant for the stock radio just without a connection to the data bus, using both switched and un switched 'hots', not 'hunting' for a 12v feed from elsewhere. Speaker leads are for speakers, nothing else.

I can see a whole different ball game if this was one of those upscale radios with all that BS included. If that was the case, it would be a no brainer to go with the 'adapter' instead of just a harness.

My main worries are the SIR (pull fues, disconnect both left & right side connectors before any work is done) and that U1128 DTC that is generated with the stock radio disconnected (which shouldn't be a problem). I will check into the DTC as far as any inspection issue.

Alarm systems and remote starters are a whole other ball game that I would never even think about trying to DIY.
 
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#15
I pulled the factory radio, plugged my code reader in (not a scanner), it showed NO DTCs'. No U1128 which, according to the SM it should of so I question the code reader at this point (first time I used it). Started the engine twice. No MIL light or any issue. Plugged that same radio back oin and no issue.

Looks as, since this is the basic radio (no preference controls) there might not be any communication to/from the data bus.