Automotive Alarm Systems
Troubleshooting automotive alarm systems can be a daunting task. This is especially true if it is 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 anti-theft protection. There are some components, switches, and circuits used by both types of alarm systems.
Control Module: A pin diagram will be necessary to diagnose the module for 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 the factory alarm systems.
Switches: Located in the door jam, a courtesy light switch illuminates the dome light and informs the anti-theft system if one of the doors has been opened. Courtesy light, trunk and hood switches are simple on/off switches that may become faulty and wreak havoc on the security system. All three of these switches are used to prevent unauthorized entry. If the switch is stuck open, the alarm would not set and remain unarmed. This will result in a dead battery if the dome light remains illuminated. An intermittent problem with a courtesy light switch will activate the alarm when the vehicle’s parked. This is a common problem with all kinds of automotive alarm systems.
Ignition Switch: Alarm systems use the ignition switch 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. It's important to take the time to splice into the ignition wire and provide a good connection that will not fail or result in an intermittent connection.