Automotive Antitheft Systems
Troubleshooting automotive antitheft systems can be a daunting task. This is especially true if it's a factory alarm or an aftermarket alarm system with 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.
Control Module: The control module is the brain of the system. Some aftermarket systems use inexpensive computer chips in the control module. This may result in a short lifespan and future problems with the module. A pin diagram will be necessary to diagnose the module for proper input and output information. Most late model factory systems are diagnosed with a factory scan tool. Not all scan tools are capable of providing information about factory alarm systems, but may show results for the courtesy switches and other vital inputs to the system.
Courtesy Light Switch: Located in the door jam, a courtesy light switch illuminates the dome light and informs the antitheft system if one of the doors has been opened. These components are used by both factory and aftermarket alarm manufacturers. These along with trunk and hood switches are simple on off switches that when worn from continuous use (driver's door) can become faulty and wreak havoc on the security system. All three of these switches are used to prevent unauthorized entry. If the switch were stuck open, the alarm would not set or may remain unarmed. This may result in a dead battery from a dome light that remains illuminated. This is as if the door were left open. An intermittent problem with a courtesy light switch will activate the alarm for no reason, like when the vehicle is sitting still. This is a common problem with all kinds of automotive alarm systems.
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. This is because things can go wrong with the installation. Working in uncomfortable positions for long periods of time 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 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 a control module. Today’s aftermarket and most factory alarms are very difficult to disarm though. It usually takes patience and the proper manuals, flow charts and directions to do so.