The Remote Keyless Entry (RKE) systems operate on 315 MHz radio signals. Therefore, they may be subject to radio signal interference -- ranging from radio towers to department store automatic sliding doors -- that will affect RKE operation. If an RKE system receives two transmissions from separate sources at the same time, it will ignore both.
During diagnosis of an RKE system with a reduced or intermittent range condition, first determine if the root cause lies with the transmitter (key fob), the receiver (in most cases, the Remote Control Door Lock Receiver) in the vehicle, or is the result of radio frequency (RF) interference.
With every button press on the transmitter, the RKE system works in conjunction with the Body Control Module (BCM) to remotely activate certain vehicle features. This is accomplished by the transmitter sending a radio frequency signal to the Remote Control Door Lock Receiver (RCDLR), which interprets the signal and activates the requested function via a serial data message to the BCM.
TIP: To prevent transmitter battery drain on later models, any RKE transmitter button(s) that is depressed longer than 30 seconds or pressed multiple times will be disabled. The disabled button(s) will remain disabled until another button that has not been disabled is pressed or if the disabled button(s) is not used for a certain amount of time.
Begin any diagnosis by first verifying that the transmitter part number is the correct model for the vehicle. There may be several transmitters used in the owner's household. The incorrect transmitter may pass the testing procedure, but it will not activate the RKE system.
As the number of electronic devices incorporated or carried in vehicles increases, so does the chance of interference and concerns of poor RKE system performance. Devices that may cause interfere with the RKE system include common items such as cell phone cords plugged into power outlets without the phone present, wireless doorbell transmitters, and garage door openers.
Typical sources of interference that may result in reduced RKE transmitter operation include:
- Proximity to radio towers, airports, police and fire towers
- Installation of some aftermarket accessories
- The presence of fluorescent lighting
- Some brands of radar detectors, CB radios, walkie-talkies, mobile radios, and cell phone chargers. These devices may be in the affected vehicle or may be in another vehicle in close proximity
- High RF traffic areas, such as shopping malls or stores with automatic doors or other RF devices
- Line of sight; the transmitter signal may simply be obstructed by another vehicle, a building or other obstructions
Since some sources of interference are based on location, be sure to ask the customer if the RKE transmitter operates intermittently or erratically in only certain locations. Ask if these locations are near radio towers, airports or other common RF sources.
Keyless Entry Tester
If a customer comments that the remote transmitter fails to operate, press each button on the transmitter one at a time while observing the vehicle systems to verify operation.
If interference is suspected, it may be possible to locate devices transmitting unwanted signals using the Keyless Entry Tester. (Fig. 2) Since the unwanted transmissions are the same frequency as the key fob, the LED on the tester will light and the audio confirmation will sound when the tester is slowly swept near the device. Be sure to sweep around all storage areas in the vehicle and under the instrument panel and seats.
Also use the tester to test the functionality of each button on the transmitter. The tester should sound a tone and illuminate the green LED when each transmitter button is pressed. If a button fails, replace the transmitter battery and test the transmitter again before replacing it.
TIP: For many 2006 and later vehicles, some functions require more than one short button press. Activating the trunk release, for example, requires pressing and holding the transmitter button before the trunk lid will release.
If the transmitter is functioning properly, program the RKE system following the procedures in the appropriate Service Information. All transmitters for the vehicle must be present when programming the system.
The RKE transmitter commands can be viewed on many vehicles using a scan tool.
Finally, a weak transmitter or vehicle battery also could lead to reduced RKE system operation. It may be necessary to resynchronize the transmitter with the vehicle if the transmitter batteries are replaced.
If only the fuel door button (some Cadillac models) or the panic button (all other models) works, this may be a sign that the system needs to be resynchronized. Follow the transmitter synchronization procedure in the appropriate Service Information.
Using the tester
Note that when you test a keyfob, not only does the LED light up, the tester makes an audible tone. If you have two or more of the same remote and one is sending a faulty signal it will sound different than the remote that works well. We use this technique every day when testing remotes. By comparing the sound to an identical remotes sound we make sure we ship out remotes sending the proper signal.
If you do not have a Keyless Entry Tester order yours now: