What is BCM? (Body Control Module)
The BCM stands for Body Control Module. It is a vehicle computer responsible for controlling body electrical systems such as lights, windows, locks, wipers, and interior electronics.
Function of the BCM
- Controls exterior lights (headlights, indicators, brake lights).
- Operates power windows and central locking.
- Controls windshield wipers and washers.
- Manages interior lights and dashboard functions.
- Controls alarm and anti-theft systems.
- Communicates with ECM/PCM via CAN bus.
Location of the BCM
- Usually located under the dashboard (driver side).
- Sometimes behind glove box or center console.
- In some vehicles, placed inside fuse box assembly.
Symptoms of a Faulty BCM
- Lights not working or flickering.
- Power windows not responding.
- Central locking failure.
- Wipers working randomly or not at all.
- Battery drain when car is off.
- Multiple electrical warnings on dashboard.
OBD-II / Diagnostic Codes Related to BCM
- U-codes (Communication faults), such as U0100–U0140 range.
- B-codes (Body system faults), depending on manufacturer.
- Loss of communication with ECM/PCM or other modules.
BCM Electrical Circuit
The BCM is connected through multiple circuits:
- 12V battery constant power
- Ignition switched power (IGN)
- Ground connections
- CAN High / CAN Low communication lines
- Multiple output control wires (lights, relays, motors)
Voltage Values
- Power supply: 12V system voltage
- Control signals: 0V or 12V switching outputs
- CAN communication: around 2.5V–3.5V fluctuating signals
- Internal regulated reference: 5V (in some circuits)
Types of BCM Systems
- Basic BCM (lights and locks only)
- Advanced BCM (full body electronics control)
- Integrated BCM (part of vehicle network modules)
Repair / Replacement Cost
- Reprogramming / coding: medium cost
- Wiring repair: depends on fault location
- Replacement BCM: approximately $150 – $800+
Important Notes
BCM faults are often mistaken for wiring or fuse issues. Before replacing, always check fuses, grounds, and CAN communication network.