This Preliminary Information communication provides information to the technician about vehicles on upgrading to Regular Production Option Code T4F high intensity discharge headlamps or additional concerns after adding after-market lighting. There are three types of issues. Customer may request a high intensity discharge headlamps upgrade. Do not attempt to upfit high intensity discharge headlamps in place of the standard halogen headlamps. This upfit is not supported by GM Engineering. Some vehicles may have a Malfunction Indicator Lamp Service Engine Soon. Before replacing any components, technician should inspect the vehicle for any aftermarket lighting that has already been installed on the vehicle. In many instances, customers have installed an aftermarket HID headlamp kit, fog lamps, or various LED exterior light bulbs in the vehicle. Remove any aftermarket lighting and return the vehicle back to factory condition before continuing with diagnosis. Also some customers may comment that when the turn signals are operated, they flash at a much faster rate than they used to. Any of these issues may be related to the use of aftermarket LED tail lamps or any other exterior lamps. Technician should reinstall the factory bulbs in order to evaluate the customer's concern.
