Brake Light Circuit Test
- When the brake pedal is applied, the brake switch circuit is completed and 12 volts is sent to a diode. The diode transmits the 12 volts to the ECU and system operation is activated. See Fig 1 .
- If there is an open in the circuit, current will be diverted through a resistor, where voltage will be reduced to about 8 volts, and then transmitted to the ECU. The ECU interprets this signal as a malfunction, turns on the warning light and ceases all anti-lock brake function. To determine correct power supply to ECU, perform checks as described in the BRAKE LIGHT CIRCUIT VOLTAGE SPECIFICATIONS (ECU TERMINAL NO. 8) table.
BRAKE LIGHT CIRCUIT VOLTAGE SPECIFICATIONS (ECU TERMINAL NO. 8)
| Application | Voltage |
|---|---|
| Brake Pedal Released | Zero |
| Brake Pedal Applied | Battery Voltage |