The light comes on when the handbrake is applied. To do this, there is a contact switch in the handbrake lever, which closes the contact when the handbrake is applied.
The pressure in the brake circuit is controlled by two brake light switches (next to the brake master cylinder). If the brake circuit loses hydraulic fluid, the pressure drops there. There is a pressure difference between two brake circuits: serviceable and faulty. The corresponding brake light switch gives an impulse to the signal light, and it lights up.
There is another version of the brake system control device: a signal is given to reduce the fluid level. In this case, the lid of the brake fluid tank has a float and a contact switch, which, when the level in the tank decreases, closes the current circuit to the lamp.
Check of the switch of a control bulb of a condition of brake system
In a car with two brake light switches, the operation of the lamp is checked when turned on: when the handbrake is released, the lamp should be on, and after starting the engine, it should go out. You can also check the so-called differential pressure reading. Proceed in the same way as when bleeding the brake system.
Fix the car in place. During the test, the handbrake must not be applied.
Start the engine and let it idle.
Open the bleed valve at the left front cylinder.
The assistant presses the brake pedal. The warning light should now flash.
Keep the brake pedal depressed. Close the bleed valve. Otherwise, air will enter the brake system.
The same check is carried out by opening the bleed valve at the front right wheel brake.
Finally check the brake fluid level; top up if necessary.
Troubleshooting in the control device of the brake system
If the control light does not go out, check the brake fluid level in the tank.
If there is not enough brake fluid, see section "Checking the brake fluid level", chapter "brakes".
Next, check whether the released hand brake lever presses down on the pin in the contact switch.
If not, disconnect the contact switch and adjust its position.
If the defect was not found, it is also necessary to check the entire length of the wire going to the control light.
If the warning signal lamp does not light up at all, this may be due to the following reasons: open current line, defect in the board and in the lamp, the contact switch sticks (only when checking the fluid level).
High beam control lamp
Only when the main beam is switched on or the light signal is switched on does the high beam warning lamp receive voltage.
Battery charge control lamp
When the engine is running, the control lamp should not light up. If the light does not come on when the ignition is turned on, this also indicates a defect. For troubleshooting, see "Troubleshooting the battery and alternator", chapter "Generator".
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