Be cautious of attaching multiple transmitters/fobs on a single key ring as RFI-related symptoms can occur. Be sure to ask the vehicle owner if the fob currently with the vehicle is the unit in which the symptoms occurred. Often a vehicle is brought in for service and the problem has been removed by the vehicle owner by separating the fob from multiple devices/transmitters attached to the same key ring. Consider the key ring illustrated in Fig. 3. This key ring could create a myriad of RFI-related performance issues that would challenge the best technician.

ALDL CONNECTOR

The ALDL (Assembly Line Data Link) connector allows access to the computer system for diagnostics. Some companies utilize that connector for other reasons such a fleet monitoring, fuel economy, maintenance intervals, performance enhancement, etc.
Consider any accessories, electrical devices, power-up devices, or fleet monitoring/tracking devices that plug into the ALDL connector, as they can influence the vehicle’s electronics. The symptoms may include driveability issues with the engine and transmission, erratic or false gauge readings, Service Engine Soon (SES) light illumination with stored trouble codes, TPMS light illumination, battery discharge due to the Bus or LAN traffic remaining active, etc. These symptoms may be challenging for the technician, as these accessory items are often disconnected by the vehicle owner when the vehicle is taken in for repairs. Make certain you question the vehicle owner, as determining the use of such ALDL devices can save a lot of diagnostic time searching for a condition that has been removed from the vehicle prior to you receiving it for diagnostics.

LOW VOLTAGE

When encountering a No Fob/No Key detected message some basic tests should be performed prior to getting too deep into the diagnostics or re-programming devices.
1) The first consideration should be the voltage level of the fob battery. A “Low Fob Battery” message is often displayed on the dash if the voltage drops below 2.6 volts for three consecutive ignition cycles.
2)The starting, lighting and ignition battery must be above 10 volts for the system to accurately detect the fob signal. Voltage in the 10-volt range can prevent entry of the vehicle. The low voltage symptoms often occur when the vehicle is not driven for a 2–3 week period, resulting in a battery discharge condition due to parasitic current drain. The vehicle owner should never leave the fob within 25 feet of the vehicle when parked. The presence of the fob prevents the computers from going to sleep, resulting in a battery discharge condition. Pay special attention to any accessories that may have been added. If wired incorrectly, they may keep the computers awake, promoting an excessive parasitic current drain and a discharged battery.