Review on Metra GMOS OnStar Interface Systems by Tyler Owens

Why is this about Pac Audio RadioPro 5 (RP5-GM11)? Because the RP5-GM11 can produce very noticeable hiss and hiss in your speakers. GMOS can fix this problem by reducing gain. There is no setting for this on the RP5-GM11. My car: 2003 Hummer H2, Bose audio system - 6-disc OEM head unit, Bose speakers and subwoofer, and "deluxe" version of the Bose amplifier. The LUX amplifier is digital and now I can advise you to know in advance which one you have before deciding on such an interface. Google Lux vs. Bose Premium Amplifier. See attached photo (sent by another installer) We are not talking about whether your car is a luxury model or not. I upgraded my main unit to Pioneer AVIC8200NEX. I installed two RP5-GM11 (the first had other shortcomings besides the noise). Whether my new head unit wiring harness was connected to the RP5-GM11 module or not, and no matter what audio source was selected, even though it was fully connected, I heard a faint hiss from all speakers, unrelated to engine RPM had to do (NOT engine whine) and imagine if the car was running or if I just started the power from the auxiliary key position. All my connections were checked again, soldered, all grounds are fine. The hissing disappeared only after the power was removed from the RP5 unit. This only happened when I decided to turn off the main unit completely. The Hummer H2 isn't the quietest car and I clearly heard the hiss while driving in all conditions. As a result of contacting PacAudio, they had no other solution but to tell me that they had tested their unit on "all trim levels" and that was the first they had heard of. They suggested I bypass the amp. However, an internet search revealed other hissing problems. Let's get to GMOS. I also bought a steering wheel controller (ASWC-1) which was easy to install as the GMOS module already has a connector for the steering wheel controller - besides connecting the red wire to the radio harness power wire, that part of it is a plug and play - my main device was recognized automatically and everything was fine. As for the GMOS connection, it's pretty simple and no more complicated than RP5-GM11. (The 24-pin GMOS harness that connects to one of the OEM radios has an orange wire going through - the installation instructions don't mention what it is for - the corresponding pinout on my OEM connector was blank anyway, I have the orange Wire plugged in and plugged in. In the end it didn't matter if you have a supplied star and whether or not you use it, I would still suggest connecting your secondary radio's "mute" wire to the GMOS harness mute wire - Star turns on whether you accidentally press the power button on your steering wheel or not, it turns off your radio.You can then watch it start over - not great if you're in navigation mode.What makes GMOS better ?1) Adjustable gain adjustment by screw. As with the RP5-GM11, both with and without the new GMOS-connected head unit, I heard speaker hiss at maximum gain gain. Turn the gain back down a bit and the hiss will go away. Amen. As for the volume; Even with the gain reduced even more than I set, the sound was still louder than the OEM. I haven't lost anything. 2) On-Star volume can be controlled directly from the steering wheel volume control - on the RP5-GM11 you had to select one of several preset levels and access the module to do this. 3) GMOS Is it possible to update the firmware with a regular micro USB cable - with RP5-GM11 you need to buy a proprietary cable. Advise anyone with speaker hiss (not engine howl) to try this GMOS instead of a Pac Audio product.