Replacing a factory-installed audio or navigation system in a vehicle like the Chevrolet Corvette C6 or Chevrolet Tahoe requires careful planning and adherence to technical specifications. The Axxess GMOS-04 wiring interface is a critical component in these installations, especially for retaining factory features such as OnStar, Bose audio, and steering wheel controls. This guide provides a detailed, step-by-step overview of the installation process, compatibility considerations, and troubleshooting tips for users who are integrating aftermarket navigation systems into GM vehicles from 2005 to 2010.
Understanding the GMOS-04 Interface
The GMOS-04 (GM Output Switch) is a wiring interface designed by Metra to simplify the integration of aftermarket audio and navigation systems into General Motors (GM) vehicles. It is particularly useful for models from 2005 to 2010, including the Chevrolet Corvette C6 and Chevrolet Tahoe. The GMOS-04 supports the retention of several factory features, including OnStar, Bose audio, and safety chimes, which are often lost during a standard radio replacement.
One of the key benefits of the GMOS-04 is its ability to provide connections for essential system inputs such as the Vehicle Speed Sensor (VSS), parking brake, and reverse signals—critical for navigation systems that rely on these inputs for accurate map display and functionality. Additionally, the interface includes provisions for high-current device control, which is necessary for managing power to the new head unit.
However, the GMOS-04 has certain limitations. For example, it does not retain factory Bluetooth functionality, which is a notable feature in models from 2009 onwards. To enable steering wheel audio control (SWC), an additional module like the Axxess ASWC-1 is required. This supplementary unit connects to the navigation head unit via a 3.5mm SWC input or a wired remote connection.
Compatibility and System Requirements
The GMOS-04 is explicitly compatible with GM vehicles manufactured between 2005 and 2010. This includes models such as the Chevrolet Corvette C6, Chevrolet Tahoe, and similar platforms. The interface is not a universal solution and must be paired with the correct steering wheel control adapter if the vehicle is equipped with factory audio controls. The Axxess ASWC-1 is the recommended module for this purpose.
When selecting an aftermarket navigation unit, users should ensure that it is compatible with the GMOS-04 and the vehicle’s existing wiring harness. The GMOS-04 provides the necessary signals for the head unit to function as intended, but compatibility with the new receiver is essential for optimal performance.
In addition to the wiring interface and head unit, the installation may require additional components such as an antenna adapter, which connects the factory antenna to the new receiver. The GMOS-04 includes a GM-to-Motorola antenna adapter, which is necessary for maintaining satellite radio and GPS functionality.
Step-by-Step Installation Guide
Step 1: Preparation and Tools
Before beginning the installation, ensure that all necessary tools and components are available. These include the GMOS-04 wiring interface, a compatible steering wheel control adapter (if needed), the new head unit, an antenna adapter, and a single-pole double-throw relay for managing high-current devices. Additionally, tools such as screwdrivers, pliers, and a multimeter may be required for disassembling the console and testing connections.
It is also important to review the vehicle’s user manual and the manufacturer’s installation guide for the new head unit. These documents provide critical information about the vehicle’s wiring harness and the specific requirements for integrating the new system.
Step 2: Removing the Center Console
To access the factory radio and wiring harness, the center console must be removed. Begin by removing the shift knob (if applicable) and the center console storage box lid. The storage box is secured with a "piano-type" hinge and four T-15 screws. Care must be taken not to over-tighten these screws during reassembly to avoid stripping them.
Next, remove the two front screws on the storage box. These are located behind round plastic covers and require a T-15 screwdriver. Once these screws are removed, un-clip the clips holding the emergency brake boot in place. This step is crucial for preventing damage to the emergency brake mechanism during the installation.
After removing the emergency brake boot, the two 7mm bolts at the front of the emergency brake cavity can be accessed. Care should be taken to avoid dropping these bolts into the cavity, as retrieval may be difficult.
The lower console trim piece on the passenger side is held in place by two metal spring clips. Gently pull down the rear of this trim piece and work it outward to remove it. A top groove along the back of the trim piece fits under the center console lip, so it may be necessary to apply slight pressure to disengage it.
Once the lower console trim piece is removed, carefully tilt the console upward and pull it back to un-clip the hidden attachments. For manual transmission models, the shifter must be pulled back to allow the console to be removed. The shifter boot should be pulled up over the shaft to facilitate this process.
Step 3: Disconnecting Electrical Components
After the console is partially removed, the hazard light and any additional switches should be disconnected. The hazard light is located behind the bezel between the HVAC vents and can be un-clipped by pushing in the side tab before disconnecting the plug. Some models may have additional switches located to the left and right of the ashtray, which are disconnected in the same manner.
The cigarette lighter connection is located on the right side of the ashtray. To disconnect it, insert a small screwdriver or wrench into the hole on its side and push in the small pin. Once disconnected, the console can be draped over the passenger seat to gain access to the 12V plug and other connections.
If necessary, the climate control unit can be unplugged and set aside to create more space in the radio cage. This step is optional but recommended for easier access during the installation.
Step 4: Installing the GMOS-04 Interface
With the console removed and the factory radio disconnected, the GMOS-04 wiring interface can be installed. The interface should be connected to the factory wiring harness using the appropriate connectors. Care must be taken to ensure that all connections are secure and properly seated to avoid signal loss or intermittent operation.
Once the GMOS-04 is installed, the new head unit can be connected to the interface. The wiring harness from the head unit should be plugged into the corresponding connectors on the GMOS-04. If the vehicle is equipped with steering wheel audio controls, the Axxess ASWC-1 module should be connected to the head unit via the 3.5mm SWC input or a wired remote connection.
After the head unit is connected, the antenna adapter should be installed. The GMOS-04 includes a GM-to-Motorola antenna adapter, which is necessary for maintaining satellite radio and GPS functionality. The antenna should be mounted in a location with a clear view of the sky, such as the left HVAC vent in the radio cage. A small steel plate is recommended to improve signal reception, and the antenna should be secured with twin stick-type foam tape.
The long wire from the antenna should be coiled up and secured with a zip tie to prevent it from interfering with other components. Once the antenna is installed, the new head unit should be tested to ensure that all features are functioning correctly.
Step 5: Reassembling the Console
After the new head unit and all connections are installed, the console can be reassembled. The climate control unit should be reconnected, and the 12V plug and other connections should be reattached. The console should be carefully placed back into its original position and secured with the appropriate screws and clips.
The emergency brake boot should be reinstalled and the two 7mm bolts at the front of the emergency brake cavity should be resecured. The lower console trim piece on the passenger side should also be reinstalled, ensuring that it is properly seated and secured with the metal spring clips.
Finally, the center console storage box lid should be reinstalled and secured with the four T-15 screws. Care should be taken not to over-tighten these screws to avoid stripping them.
Troubleshooting and Common Issues
Despite careful installation, users may encounter issues with the new system. One common problem is audio cutoff, where the sound cuts off for a few seconds every 15 seconds. This issue has been reported in some installations and may be related to the Bose amplifier in the vehicle. Bypassing the Bose amplifier is one potential solution, but it should be attempted with caution as it may affect the overall sound quality.
If the system is not functioning correctly, it is recommended to double-check all connections and ensure that the GMOS-04 and any additional modules are properly seated. A multimeter can be used to test for continuity and ensure that all signals are being transmitted correctly.
Conclusion
The Axxess GMOS-04 wiring interface is a valuable tool for integrating aftermarket navigation systems into GM vehicles from 2005 to 2010. By following the step-by-step installation guide and ensuring compatibility with the new head unit, users can retain essential factory features such as OnStar, Bose audio, and steering wheel controls. Careful attention to detail during the installation process is crucial for ensuring optimal performance and avoiding common issues such as audio cutoff or signal loss.
For users who encounter difficulties during the installation, troubleshooting steps such as checking connections and bypassing the Bose amplifier may be necessary. With the right tools, components, and a clear understanding of the installation process, users can successfully upgrade their vehicle’s audio and navigation system while maintaining the integrity of the factory components.