Diagnostic Information on Navigation Radio Aftermarket Modules Causing Various LAN Communication Concerns, DTC, No Crank, Vehicle Stability Lights/Messages, TPM Warning Lights, PRNDL Position Errors

This bulletin is being revised to add the 2008 model year, the Sierra model and clarify/add information (in italics). Please discard Corporate Bulletin Number 07-08-44-004 (Section 08 -- Body & Accessories).

Some customers may comment of one or more of the following concerns:

Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed LAN communications with the Tech 2®.

These conditions may be caused by the installation of an aftermarket navigation radio module.

It has been brought to our attention that some customers may be installing and using certain aftermarket products that are used in conjunction with the factory navigation radio systems.

These aftermarket products allow the user to display the video output of the DVD player on the navigation screen while driving the vehicle. Normally the DVD output is only available on the navigation display when the vehicle is placed in PARK. These aftermarket products may include additional features such as an aftermarket camera or a second backup camera. These products may enable other navigation functions to operate while driving that would normally be available only when the vehicle is placed in PARK.

Dealers have found that these products can cause unusual problems that are difficult to diagnose. These products may be difficult to identify because they are installed behind the navigation unit and are not visible unless the navigation unit is removed.

Technicians may also find aftermarket ipod interface modules installed on the vehicle. These modules may cause intermittent XM reception or the tab on the navigation screen for XM disappears intermittently.

If you suspect that the customer has installed aftermarket products of this nature and you suspect that the product may be the cause of the concern, you should ask the customer if any vehicle modifications have been made.

Additionally, if the customer's information is not available, you may want to test the navigation and DVD system to see if normally blocked functions are available with the vehicle in DRIVE. Removal of the navigation radio will also allow you to verify if one of these products has been installed.

Warranty coverage does not extend to problems created by aftermarket devices. Damage to normally covered systems caused by aftermarket products is the responsibility of the customer or the aftermarket installer.