Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Body Control Module (BCM)
The body control module (BCM) monitors several inputs in order to arm and disarm the CTD system. The BCM controls the alarm function outputs.
When the BCM detects an unauthorized entry, any door opened, the BCM applies ground to the horn, the park lamp and the headlamp relays. The BCM will send messages to the security telltale in the instrument cluster through the Class 2 serial data link. The BCM has the following 8 basic modes for operating the CTD system. The more detailed descriptions are below.
- Off state
- Idle state
- Disarmed state
- Ready-to-arm state
- Arm initiated state
- Arm delay state
- Armed state
- Alarm state
The BCM has the following 6 discrete inputs in order to monitor the CTD system:
- Ignition 1
- Driver door latch, door jamb switch
- Passenger door latch, door jamb switch
- Door lock relay
- Door key switch
- Passenger door unlock relay
The BCM applies ground once per second for approximately 2 minutes, or until a valid input to disarm the system is received by the BCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.