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.
Principle of Operation: BC1
Based on input received the BC1 energizes the appropriate internal relay to power the window up/down. The BC1 monitors the current draw of the motor at 2 ms intervals for the first 50 ms and then at 100 ms intervals.
The peak current measured is reduced by 4A and this value is then used as the cut-out current at which the BC1 will deactivate the motor. During operation of the window motor, if no cut-out current is seen the BC1 will switch off the motor after 15 seconds.
If at any point the current exceeds 35A the BC1 will deactivate the motor immediately.
| Power Window Current Monitoring | |
|---|---|
| Peak Current | =Current value at start-up of motor |
| Stall Current | =Current value at which the motor stops |
| Cut-Out Current | =Peak current minus 4Amps |
Workshop Hint
If a relay is stuck on, a fault is detected and the BC1 will switch on both relay contacts so both outputs are at equal potential and the motor stops. This is to prevent the windows from moving if the fault disappears when in sleep mode.
If current is detected when the relays are inactive, then both relays will be switched on to protect the current sensing resistor from being damaged before the fuse blows.
The current sensing resistor is used as a measuring medium- the point from where the current measurements are taken.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.