View Full Version : Head Unit Doesn't Turn Off

09-29-2011, 04:44 PM
I have a 2006 Trailblazer. Usually the radio turns off when the door is opened, but today it didn't. I had to turn the power off. I installed the head unit over a month ago and everything has worked fine.

I searched online and read that it could be the switch in the door, but the dome lights come on when the door is opened, and I also tried opening other doors but it stayed on. Also, when I start the car, the radio turns off and then back on like it usually does.

Is it possible that something inside the unit has gone bad and causing this? I haven't checked the wires behind the radio yet to see if something came apart, its just weird that this happened all of a sudden.


09-29-2011, 04:51 PM
How is the red wire for the headunit (turn on) wired?

09-29-2011, 04:57 PM
Yeah I had an issue with my current ride, it used to be the radio played on accessory, replaced the stock and now it plays just slightly after you turn the car off....so I have to have the key half way between acc. and on and I don't know why that is.

09-29-2011, 05:01 PM
I used a Scosche wiring harness, so I just matched the colors from the Radio to the harness and everything worked until now. I cant remember the exact model number of the harness, but it came with the box to keep the chime working and had a red wire.

10-04-2011, 11:57 AM
Well, from my experience with chevy's, I would have to bet that the turn on wire is not wired in correctly. I worked on my buddy's '04 Impala (w/o a wiring harness) and got into all kinds of problems. There is no stock turn on wire on most of the newer chevy's, so in his case, he had to turn it off every time that he exited the vehicle. From your description on yours, and my experience on the Impala, I would have to say that you have your constant and turn on both wired into the constant from the stock radio. By doing that, you bypass the stock turn on, which you don't have, and the radio can constantly be on. (actually kinda cool b/c you dont have to have your car on to listen to the radio :crazy: ) Then, in another friend's '01 Monte, we went the "right" way and installed a GMOS with it, to keep the door chimes, onstar capabilities, and to not have to mess with a remote turn on. I would suggest the GMOS, even though it is pretty pricey. GM Factory Integration Adapter General Motors data bus interface (model GMOS-LAN-02) Retains OnStar and factory door chime with aftermarket radio in select GM vehicles at Crutchfield.com (http://www.crutchfield.com/p_120OSLAN02/GM-Factory-Integration-Adapter.html?search=gm+wiring+harness)

Also, one other suggestion you might try, I know that some times you can just find a wire to tap into that is considered a turn on. A lot of times, i've seen the windshield wipers used for this. Basically, anything that works when the key is in the "on" or preferably "acc" position and doesn't work when the car is off should be able to work for this. I know that got kind of wordy, so PM me if you need help.

10-05-2011, 03:35 PM
I figured out the problem. The wiring harness I used came with a box to create the chime and turn on wire. Apparently the box went bad. I noticed my chime wasnt working anymore also. I replaced the box and also found a wire in the steering wheel column to use for the turn on wire instead of relying on that box. The only thing is that the radio used to stay on after turning the car off until a door was open, now it turns off with the car. But that is not a big deal to me.

Thanks for the help though.


10-06-2011, 02:14 PM
2000+ GM uses the Class II Data Bus and that is why you have to have the GMOS interface for things to function properly. your RAP (retained accessory power) is only available though the bus. this is why your radio no longer stays on until you open the door - you bypassed that system when you wired to the steering column ignition.

What is Class 2 databus ?
Affects of removing Class 2 from your vehicle
Factory Deck Removal Process
ABS Concerns
Affected Vehicle List
What About OnStar ?
New Peripheral Interfaces Available


What is Class 2 databus ?

The Class 2 system is a Serial Data Link used by GM in its vehicles, and is based on the SAE J1850 protocol, which is widely used in the U.S. It is through this data link that the body control module (or BCM) receives information and commands that are essential in determining its mode of operation.The BCM is connected, through Class 2 wiring, to the instrument panel cluster (IPC), the powertrain control module (PCM), the data link connector (DLC) and the radio.

Recently GM has now included the driver’s door module, passenger’s door module, rear seat audio controller, vehicle communication interface module or OnStar®, steering wheel audio controls, rear seat entertainment (RSE), CD changer, radio, DVD/Video, amplifier and XM radio as part of Class II. Since these new modules are part of the audio system and security system, you are now hearing more about Class II.
Connected to this same data wire is the Body Control Module (BCM), Powertrain Control Module (PCM), Transfer Case Shift Control Module, Heater & A/C controls (HVAC), Inflatable Restraint Sensing and Diagnostic Module, Theft Deterrent Control Module, Memory Seat Module, Drivers Information Center (DIC), Key/Lights/Seatbelt Chimes (most vehicles), Instrument Panel Cluster (IPC), Suspension Control Module, Electronic Brake Control Module (EBCM) and other modules.


Affects of removing Class 2 radio from your vehicle

Vehicle Customization Menu Options:
( Most Cavaliers, Sunfires and other base models do not offer most, if any of these features.
Check the vehicle owner’s manual to see available features. )
Displays current settings
Oil life monitor reset
Tire inflation monitor reset
Delayed headlamp illumination
Automatic door lock and unlock
Remote visual/audible verification of remote lock/unlock
Enable/Disable content theft
Enable/Disable trunk lock shock sensor
Short or long horn with remote lock/unlock
Key fob transmitter programming
The radio is used as a control panel to communicate with the vehicles computer for the customization of certain “convenience features”. All features work and remain at current settings with the factory radio removed, but can only be customized and/or reset by an authorized service center. More important than the above features and chime, there is no switched 12vlt. power supplied in the radios plug, so it will need to be sourced somewhere else such as the factory fuse panel. A 10A to 30A fused accessory power source is recommended. Depending on the vehicle there are several choices in the factory fuse panel, such as the sunroof or windshield wipers.

What About OnStar ?

When you remove a radio from a vehicle with OnStar ( application list below ) you loose the speaker capabilities of the OnStar system. Ventura & Metra have teamed up to make a peripheral interface for the OnStar system if you want to remove the factory radio and retain the functions of the OnStar.

Frequently asked questions

Do all these modules communicate at the same time?

Yes they do. Each module on the bus has its own ID number and is sent out every two seconds as a state of health message (SOH) to let other modules know that it is present. Every module sends information to other modules when needed. When the ignition is first turned on, there could be as many as 100 or more messages sent on the data bus from various modules within 1 or 2 seconds.

How can all the modules communicate at the same time and not interfere with one another?

Well first, all the modules have a Data Link Controller (DLC) chip with and internal or external transceiver physically connected to the data bus. And second, each module is assigned a different level of priority. The DLC is the key to the Class II bus. It is designed to send and receive data depending on priority. When each modules sends information over the data bus, they also check to see if there is other data activity on the bus. If that module sees other data while it is sending data and it has low priority, it will stop sending and try again when the data bus is inactive.

What happens if one module goes bad or power is disconnected from it? Will it load down the data bus and disable crucial control modules like the PCM or BCM?

Again, the DLC chip or transceiver is the key. It is designed so that even if power is interrupted or it damaged, it will not affect the data bus. So lets say if the radio power was disconnected but it was still connected to the data bus, it will not interfere with any other control module’s communication on the data bus.

Does your product use the DLC chip?

Yes they do. We incorporate it in our products to insure your safety when you drive your vehicle. You may pay alot more for our products for Class II, but is your life or family worth saving a few dollars?

10-06-2011, 02:14 PM

Is it true that the factory radio is related to the airbags?

No. The factory has nothing to do with the airbags or any other modules. The airbags are controlled by the Inflatable Restraint Sensing and Diagnostic Module.

Why are the factory radios being relocated when installing an aftermarket stereo?

Some vehicles have chimes built into the radio. When ever the key is left in the key cylinder or parking lights left on, the radio sends audio chimes to the speakers or to amplifier (if equipped). If the radio is removed, there is no way for chimes to be heard. Seat belts are part of the chimes also, and if not retained could result in the driver not using the seatbelt. The retailer installing an aftermarket stereo could be liable for injuries if the driver was to get into an accident and not wearing a seatbelt.

Can using a test light on the data bus cause damage to modules on the bus?

No, the DLC chip or transceiver is short circuit protected to ground and to voltage spikes up to 40 volts. The worst thing that will happen is that modules will not be able to send SOH messages and data information. Basically the engine won't run unless the BCM, PCM and other modules can communicate to each other.

I've heard that one vehicle would not start if the factory radio was removed. I thought the radio has nothing to do with any engine control modules?

Currently we have not run into a vehicle that has this configuration and we wonder if the installer had a wiring issue that may have disabled the data bus?

I tried to put a LOC at the headunit but the volume of the aftermarket amplifier does not vary with the radio volume. Why?

Some vehicles have fixed audio signal outputs going to the factory BOSE amplifier. The BOSE amp only accepts 2 channels of audio from the front outputs of the factory radio. The rear outputs of the factory radio go to the RSE. When you adjust the volume/fade/balance or even EQ settings, the factory radio sends data to the factory amplifier. The factory amplifier actually does all the fading/balancing and adjusts EQ settings direct

10-06-2011, 02:17 PM
i recommend you replace the failed GMOS adapter.