Scosche GM21SR Stereo Replacement Interface
For 2007-Up Select General Motors Vehicles with OnStar® High-Speed LAN
Product Overview
The GM21SR digital interface allows connection of an aftermarket radio to GM vehicles equipped with standard Bose® and OnStar systems. It is designed for use with any aftermarket radio.
Application Guide
See important application information below:
| Make | Model | Year(s) |
|---|---|---|
| Buick | ||
| Cadillac | ||
| Chevrolet | Impala | 2006-07 |
| Silverado (new body style) | 2007 | |
| Tahoe | 2007 | |
| GMC | Yukon | 2007 |
Application Notes: Not for use on Premium Bose Sound Systems (includes Y91/z75 Bose). Code may be found on the service parts sticker (normally in the glove box).
Retained Factory Features
- Standard Bose® audio
- OnStar®
- Warning Chimes
- Park Assist (front/rear)
- Heated Seats
- A/C Fan Speed
- Folding Mirrors (including reverse)
- Turn Signal (clicker)
Some features may need to be turned on using factory menu options.
Preliminary Instructions & Warnings
Before Beginning: Read this entire instruction manual first.
Caution: Disconnect the negative battery terminal to avoid short circuits. Read all manufacturer warnings regarding airbags and electrical systems in your vehicle. Use of a volt/ohm meter or computer-safe LED probe is recommended for checking wiring. A test light or grounded light probe used improperly can damage the vehicle's computer and/or diagnostic system.
Important Connection Information
Connect the audio input & output plugs according to the factory audio system type. Use plugs marked "STANDARD SPEAKER SYSTEM" if the factory system is not amplified. Use plugs designated as “BOSE AMPLIFIED SYSTEM" if the vehicle has a standard amplified or standard Bose sound system.
Diagram Description: The interface module has two sides. One side connects to the vehicle harness (labeled "THIS SIDE TO VEHICLE HARNESS") and includes connectors for Non-Bose System, Standard Bose, and an 8-Pin connector. The other side connects to the aftermarket harness (labeled "THIS SIDE TO AFTERMARKET HARNESS") and includes connectors for Non-Bose System, Standard Bose, and a 10-Pin Power Connector, along with a Chime Speaker output.
Installation
- Disconnect the negative battery cable to avoid short circuits.
- Remove and unplug the factory stereo. Contact Scosche Tech Support for specific removal steps if needed.
- Match and connect the GM21SR harness wires to the appropriate wires of your aftermarket stereo's plug. For example, connect the +12V yellow constant lead from your stereo to the yellow wire on the GM21SR harness. The red +12V accessory wire from the GM21SR module is rated at 5 Amps Max for a single aftermarket car stereo. Connecting additional accessories to the red wire can damage the GM21SR module. Wire color codes are designed to match most aftermarket car stereos.
- Tape all unused wires to prevent short circuits.
- Reconnect the negative battery cable.
- Connect the 14- and 16-Pin female harness to the factory 14- and 16-Pin plugs.
- Connect the 8- and 16-Pin male connector to the GM21SR interface according to the factory audio system. A warning chime will be heard.
- Connect the 10- and 12-Pin connectors to the GM21SR interface according to the factory audio system.
- As you install your new stereo, place the GM21SR module in the rear of the dash cavity behind the stereo. Cable ties or double-sided tape can be used for securing (not included).
- Start the vehicle and confirm the radio turns on and audio is heard.
Wiring Diagram & Color Codes
Diagram Description: The wiring diagram shows the connections between the Aftermarket Radio Harness, the Interface Connector, and the To Car Connector. It details specific wire connections like RED (ACCESSORY +12V), YELLOW (CONSTANT +12V), BLACK (GROUND -12V), BLUE/WHITE (AMP REMOTE), etc.
Wire Color Codes:
- White: Chassis Ground (-12V)
- White/Black: Left Front Positive (+)
- Green: Left Rear Positive (+)
- Green/Black: Left Rear Negative (-)
- Violet: Right Rear Positive (+)
- Violet/Black: Right Rear Negative (-)
- Gray: Right Front Positive (+)
- Gray/Black: Right Front Negative (-)
- Black: +12 Volt Battery Constant
- Yellow: +12 Volt Ignition Switched
- Red: +12V Remote Output
- Blue/White: Amp Remote, Radio ON Signal
- Orange: Illumination Output (Optional)
- Brown: Phone Mute (Optional)
The color codes conform to E.I.A. standards but may differ from your specific car stereo. Always refer to your stereo owner's manual for wiring details. Insulate unused wires to prevent damage.
Installation Note: High-Power Stereos
Aftermarket high-power stereos can overload the Red +12V ACC wire from the interface module, potentially causing the output to shut off randomly. To correct this, connect a relay to the interface's Red Accessory output wire and a fused +12V power source to power the aftermarket head unit. The diagram shows a relay with terminals 87, 85, 86, and 30, connecting the fused +12V, ground, the interface's red wire, and the aftermarket radio's red ACC input.
Operation
- With the engine running and audio playing, press the OnStar button (if equipped) to confirm functionality. Then cancel/turn off OnStar; audio should resume.
- With all doors closed, turn the key to the OFF position. Retained Accessory Power (RAP) will keep the radio on.
- With the key in the ignition, open the driver's door. Audio will turn off, and a warning chime will be heard through the GM21SR built-in speaker.
- Turn the key to the “ON” position (start vehicle). Test left/right turn signals (audible clicking from turn signals).
- If your vehicle is equipped with Parked-Assist: Disengage the parking brake. Have someone stand behind the vehicle (at a safe distance) and put the vehicle in reverse. Confirm by having someone walk towards the sensors. Put the vehicle back in the parking position.
- Confirm remaining options if equipped (listed on the front page).
Adjust OnStar Volume:
With the engine running, press the OnStar button. Use the steering wheel volume UP/DOWN buttons (if present) to adjust volume. If not available, with OnStar activated, slowly turn the dimmer knob clockwise to adjust volume UP or DOWN.
Adjusting Warning Chime:
The GM21SR interface allows adjustment of the chime audio level (soft to loud). Follow these steps:
- With the ignition key OFF and resting in the ignition, turn on vehicle headlights.
- Open the driver's door. A reminder chime will sound, indicating the key is in the ignition and lights are on.
- Slowly rotate the dash illumination dimmer knob to adjust chime volume. Turn the knob up to increase volume or down to decrease.
- Once the desired volume is achieved, turn off headlights and close the door. Your chime setting is stored by the GM21SR. You can re-adjust the dash lighting dimmer level with the door closed and headlights on.
Troubleshooting
Problem: Vehicle does not recognize the interface
Tip/Solution: It is recommended to turn the ignition key to the "RUN" position for approximately 5 seconds and then OFF before beginning the first test of the newly installed interface.
