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Dealer Dignosis says after market stereo prevents communication with ECM. BS or not?

I also pose this question on another post in regards to my past brake issue.

I had a wierd pulse in my brake pedal the first time I would press the brakes from a cold start. I had several people tell me this was my imagination, but I was pretty sure it was not. After a recent brake job, I was unable to get the pedal stiff and my 2006 Mallibu Maxx has an ABS system which requires a GM computer to do a ABS bleeding procedure so I grudgingly brought the car back to the dealer for a pro-bleeding, with their fancy computer. They called me and said that they could not communicate with the computer on the car, and would need to do a full “Diagnostic” to determine why.

What they found, or claim to have found, is that my after market stereo is the cause for this. I’ve had my Sony stereo installed in the car almost as long as I’ve had it, for 5 years, and I’ve never had a problem, or had anyone tell me this was a problem. They were able to communicate once they disconnected it and they completed the bleeding.

Since I’ve gotten the car back the pulse in my brakes is gone, it hasn’t done it once in over a week. I’ve also noticed that my cruise control now works again, it hasn’t worked in while, but I almost never use it so I’ve hardly even noticed it or thought to mention it.

Now here is my new question, Should I believe that the stereo is really the issue, or is there something else, that has caused these glitches, and the stereo just happens to tie it all together.

Clearly, you need to take the next step, which is obviously to re-connect the stereo. Find out whether the problem returns or if it is gone for good. Let us know.

Hard to believe that a car radio needs to be on the same communication’s bus as an ECM.
Whomever installed that stereo may have messed up installation.

I know that some of those guys don’t look at the schematic but often just use sharp probes to poke into the wire to find the levels they need.
For instance, maybe they needed a ‘on while running’ signal and found one that looked like what they were looking for when they probed into one of the communication wires.

GM cars & trucks use the speackers for the door chime and headlamp reminder so yes they do talk to each other

Well, there^ you go. I was thinking they may have tapped into the CAN bus somewhere but splicing into a speaker line that’s driven from somewhere else isn’t a good thing.

If they indeed wired the systems in parallel, I guess one could put a relay in the line that switches the speaker from ECM to radio and uses the ‘switched power’ to switch the relay. That way, when you take the key out, the radio will be switched off the speakers and the ecm can still play its sounds through the speaker.
It is a bit of a hack but would probably work if you need to use an aftermarket radio. Come to think of it, I bet the GM radio probably uses a similar mechanism to make their system work.

It’s not BS. A radio or similar electronic device must be connected properly using the factory plug. In my case it was a “brake controller” for a trailer. Welcome to the world of computerized vehicles.

Sure it’s possible and I’ve seen it. In addition to the above about the warning chimes, the radio also shares data lines with engine and body control systems so the radio volume will increase based on vehicle speed, keeping the level steady from idle to freeway speeds. Since the radio is part of the Vehicle Speed Sensor communication, it also makes sense that this disabled the cruise control and possibly affected ABS communication.

I also think the radio is part of the anti-theft system, but I’m not sure at the moment.

I too support the idea that the installation was improperly done. This is a serious and not uncommon problem.

Automotive electronics is not as simple as you may think. My electrical manual at home for my car is about 200 pages (I printed it… I like hardcopy…hate working off screens). Butchering a harness can cause all forms of wierd malfunctions. Simply putting something in series rather than parallel cuts the voltage available to the component that the circuit was intended to support. I just paid $60 for a stupid little wiring haness just to install fog lights, because I refuse to cut into a good harness…and the manufacturer wil not sell only the connectors.

Let me offer a suggestion. How butchered up is the OEM harness? If the OEM connector is still intact and they connected with clamp splices (now disconnected I’m sure), you might be able to get an adapter for your car, connect it to the aftermarket unit (the adapter comes with instructions), and plug the unit dorectly onto your OEM harness. That’s the ONLY way an aftermarket unit should be installed.

By the way, just the fact that everything is working right now is evidence that what they told you is true and accurate. You should be happy with them rather than skeptical.

Aftermarket stereos are getting harder and harder and, many times, completely impossible to do.
Far too much computer interface these days that can’t be replicated.

un-install and start fresh at square one to see if anything can be done differently.

If not, you’re s.o.l. and need to return to o.e.

The radio is now an integral part of the overall electronics package. Distributed resources and all that…
You can search about it on your own but here is one link that gives some insight into the new world of automotive electronics-

GM puts a lot of functionality into their OEM radios. Replacing one is not a simple task like it used to be. It’s not a matter of wire-oring the speaker wires, commands are sent to the radio and it responds with the appropriate output. The radio is also matched to the specific vehicle by the VIN…

Here. Perhaps perusing through the attached will give you an idea how complicated it can get. And it gets worse every year.

Unless an aftermarket radio simply plugs into the existing connectors made for that purpose, no slicing and splicing please, you are asking for trouble…You are lucky the dealership was able to diagnose it correctly and cure your brake problem…Many times, that would not have happened…

Actually, the audio system on that car looks very standard, unless there are connections they aren’t showing…

But the question remains…did they connect it to the system properly?
It would appear the answer is NOT!

Oh, there’s no question that they screwed up - absolutely.

I just installed a android nav, gps, wifi, bluetooth, touchscreen, dvd car stereo in my 2007 mustang gt. Fresh from China, This thing has everything. I can even surf the net. So I’m having all kinds of can bus problems with it. odd problems not related to the car stereo… been researching the can bus system and it seems that address conflicts can arise from aftermarket canbus controllers. I’m going to remove the canbus controller from the factory ford radio and use that. Chop Chop.

The dealership computer probably runs a scan on the vehicle to see if it is still intact and as mfg by GM. I’m guessing here but it may have a zero tolerance for items that are missing off the CAN Bus.

Like @missileman stated… welcome to computerized cars.

Its getting silly out there people…