Automotive Antitheft Systems
Troubleshooting automotive antitheft systems can be a daunting task; this is especially true if there is no installation information available. Factory alarm systems typically incorporate the control module into the BCM or PCM. Aftermarket alarm systems add an additional module to the vehicle and tap into circuits and switches to provide antitheft protection. There are some components, switches, and circuits used by both types of alarm systems.
Courtesy Light Switch: Located in the door jam, the courtesy light switch illuminates the dome light and informs the antitheft system if one of the doors is open. Both factory and aftermarket alarm manufacturers use these switches. Unfortunately, these, along with trunk and hood switches, can become faulty and wreak havoc on the security system when worn from continuous use (driver's door).
All three of these switches prevent unauthorized entry. If the switch were stuck open, the alarm would not set or remain unarmed. An intermittent problem with a courtesy light switch activates the alarm for no reason, like when the vehicle is sitting still. This problem may result in a dead battery from the alarm or dome light.
Ignition Switch: The ignition switch is another component utilized by both aftermarket and factory alarms to disable the starting system. Splicing into the ignition switch presents more problems with aftermarket systems than with factory alarms. Things can go wrong with the installation. Working in uncomfortable positions for long periods can make installation more difficult.
These are just a few components used by antitheft systems. A faulty inhibitor or start relay could be at fault. So often, the key pod or the ignition switch's antenna ring or module is preventing the system from operating or even shutting down.
In the past, temporarily disarming a system may be as easy as flipping a switch or unplugging the control module. Good or bad, today's aftermarket and most factory alarms are very difficult to disarm. It usually takes patience and the proper manuals, flow charts, and directions to do so.