I came accross this and thought you guys might find it helpful;
Document ID: 2079887
#08-08-47-001: Keyless Access System Description, Operation and Possible Customer Concerns - (Mar 13, 2008)
Subject:Keyless Access System Description, Operation and Possible Customer Concerns
Models:2004-2008 Cadillac XLR, XLR-V 2005-2008 Chevrolet Corvette
Attention:A copy of this bulletin may be given to your customer to assist you in explaining the proper operation, features and possible symptoms of external radio frequency interference on the Keyless Access System.
Don't Do This
Read this bulletin and offer the information to your customers.
Do not replace the remote door lock receiver.
This bulletin is designed to offer some guidance on the expected and proper operation of the Keyless Access System. The Keyless Access System is essentially both a "wireless" and portable technology that transmits and receives radio frequencies. These types of technologies, whether being your cell phone, a wireless computer, or other electronic devices, are susceptible to external interference which may temporarily affect system performance. This does not indicate that any defect in the system exists, nor should any components be replaced for this type of concern. The information below will further acquaint you and your customer with the identification of external interference and the back-ups available to easily restore expected system operation. System Description
The Keyless Access System is a vehicle entry and starting system that allows you to operate the vehicle without removing the key fob (transmitter/receiver) from a purse or pocket. With the vehicle locked, the operator simply walks up to either door and squeezes the door handle switch. If a known fob is recognized, the door will unlock and open. After entering the vehicle (with a valid fob), the owner presses the brake pedal, and pushes the start button. When the fob is recognized, the vehicle will start. Explanation of Passive Entry
A passive entry event is one where the fob is automatically recognized when the door handle switch is activated (no buttons are pressed on fob to unlock door prior to opening). Passive door unlocking can be configured in the DIC personalization menu so that just the driver door unlocks when a passive entry event occurs or both doors unlock. When doing passive entry at the passenger door, both doors will always unlock.
The vehicle has several antennas inside and outside the vehicle to detect if a fob is present. For example, when the driver door handle switch is pressed, the vehicle first transmits a signal to any fob on the INSIDE of the vehicle to NOT respond. This is called a sleep command. The sleep command temporarily instructs any fobs on the inside of the vehicle not to respond to the door antennas. The sleep command is used so that if you have someone sitting in a locked vehicle with a valid fob, the fob inside the vehicle will not allow a door to open from the outside handle switch. After the sleep command, the driver door antenna turns on so that it can detect a fob on the outside of the driver door. If one is found, the door is unlocked. Possible Concerns
Whenever you are using a complex radio frequency system to judge proximity and location, there are certain limitations and variables that may arise. Both the vehicle architecture (fiberglass body) and the environment surrounding the vehicle may contribute to some variability in system performance. A common possible concern is when the sleep command extends just slightly outside the vehicles interior. Under this scenario, the door may not open when a fob is very close to the door handle switch (refer to the graphic below). Moving the fob away from the handle switch will restore normal system operation. Passive Entry Zones
(1)Entry Area(2)Potential Inactive (Overlap) Area (3)Sleep AreaRefer to the section on "Interference" below for other issues that may cause problems with passive entry. Vehicle Starting
Again, there are several antennas in the vehicle that detect the fob’s presence in the vehicle’s interior. These antennas are turned ON by relays in the controlling module. A slight clicking noise or chatter may be heard when the antennas are turned on. This is a normal and expected system function.
When the start button is pushed, the antennas are turned ON so that they may detect a fob on the inside of the vehicle. If a valid fob is found, the vehicle is allowed to start. The starting range may extend slightly outside of the vehicle, but not more than 10-12 inches (25-30 cm).
Refer to the section on "Interference" below for other issues that may cause problems with vehicle starting. Interference
The Keyless Access System relies on radio frequency (RF) signals to allow passive entry and starting. It is possible that other devices may interfere with the RF signals. These types of devices include (but are not limited to) cell phone chargers, two-way radios, power inverters, computers, etc. The most common type of interference is from cell phone chargers (regardless of whether the cell phone is plugged into it or not). High RF traffic areas, such as gas stations which use pay-at-the-pump RF transponders, may also cause interference that could lead to a customer perceived malfunction.
The Keyless Access system operates by using two separate radio frequencies. Important: GM’s devices conform to all FCC and Industry Canada regulations. Not all radiating devices that are sold publicly conform to the same regulations and can cause interference with the system’s operation.
The way to determine if devices inside your vehicle are interfering with the Keyless Access System is to hold the fob directly next to the suspect device and press the start button. If the DIC displays "No Fob Detected," this device is likely causing a disruption to the system. Usually, keeping the fob farther away from the device will correct the problem. Changing parts in the system (fob/receiver) will normally not correct this issue. The source of the interference must be eliminated.
Occasionally, it is possible to be in an area where external interference is present. For instance, parking directly under a radio transmitter tower may cause issues with entry or starting. The vehicle is equipped with backups and safeguards to assist you in entry and starting. Passive Entry
If interference is present, it may be difficult to passively enter the vehicle by squeezing the door handle switch. If this is the case, try pressing the unlock button on the fob. If the door still will not unlock and open, use the mechanical key to unlock the trunk/hatch. The rear key cylinder is located in the rear fascia for the XLR and directly above the license plate in the Corvette. Once the rear trunk/hatch is opened, there is a door release cable on the left side of the trunk interior. Pull this handle to pop the door open. rvette Hatch Lock Cylinder Location
XLR Trunk Lock Cylinder Location
No FOB Detected DIC Message
Try moving the fob to different locations within the vehicle. If moving the fob to different locations does not help, place the fob in the glove box fob pocket with the buttons facing to the right and then press the START button. As long as the vehicle’s battery is sufficiently charged, the vehicle will start. FOB Detection Pocket/Slot
If this feature is turned on, the vehicle will notify you with three quick horn chirps, indicating that a fob has been left in the vehicle. This feature operates after the vehicle has been turned off, the driver door has been opened, and then closed, and two seconds elapse. After the two second timer cycle, the vehicle looks for the fob on the interior of the vehicle. (Keep in mind that the fob may be determined to be "inside" of the vehicle even if it is slightly outside.) In order to avoid getting the Key-In Reminder warning, make sure the fob is moved so that it is at least 1 foot (30 cm) outside of the vehicle when closing the door. Upon opening the driver door after the Key-In Reminder warning activates, the Key-In Reminder chime will sound. This is normal.
Although the Key-In Reminder warning (horn chirps) only occurs after the first driver door closure, all subsequent opening and closing of the driver door will still cause the Key-In Reminder feature to search for the fob on the inside of the vehicle. Passive Door Locking
If this feature is turned on, the vehicle will automatically lock itself after all doors have been closed, a slight delay has occurred, and at least one fob has left the vehicle. For example: when the engine is turned off, the vehicle counts the number of fobs on the "inside" of the vehicle. When the driver door is opened and then closed, there’s a delay of two seconds before the vehicle searches for fobs on the "inside" of the vehicle again. If the number of fobs has been reduced by at least one, the doors will lock eight seconds later. If the number of fobs has not been reduced, the vehicle waits eight seconds and then counts the number of fobs on the "inside" of the vehicle one last time. Again, if the number of fobs has decreased by at least one, the doors will lock. If no fobs have been removed from the vehicle, it will not lock. This feature can be personalized so that it is "off," "silent" (lights will flash) or "horn."
As described previously, interference can disrupt the system. If interference disrupts the system, the fob may not be detected, causing the vehicle to lock. To avoid accidental locking of the vehicle, do not leave a fob on the inside of the vehicle when passive locking is enabled. To turn off passive locking for one ignition cycle, press the unlock switch on the driver door until a double beep is heard with the door open and the vehicle off. Passive locking will not re-enable until the next time the ignition is turned on. Personalization
The system utilizes information based on the current driver ID. The driver ID will change based on several actions: Tip
The driver ID controls are located on the driver door.
If the "1" is pressed, the driver ID will change to driver 1 settings. If the "2" is pressed, the driver ID will change to driver 2 settings. When the driver door is opened by using the passive unlocking feature, the lowest numbered fob will control the driver ID. For instance, if fobs 1 and 2 approach the driver door and a passive unlock is performed, the driver ID will change to driver 1 settings.
Any time a button is pressed on the fob, the driver ID will change. For instance, if driver 2 approaches the vehicle and presses the unlock button on the fob, the driver ID will change to 2 (even if driver 1 has just entered the vehicle by doing a passive unlock event).