|LANCE’S CORNER – AUTO REPAIR HELP|
AUTOMOTIVE WARNING LIGHTS
Charging systems commonly use a warning light that uses a system called the balanced circuit. The warning light receive battery voltage on the input side of the light, while the ground side is connected to the alternator output circuit. When the key is on, and the engine is off, current will flow through the light and ground inside the alternator. When the engine is running, current will flow out of the alternator output circuit and will stop current flowing through the warning light by equalizing voltages on either side of the bulb.
Warning lights are used by vehicle control modules to inform operators of system failure or malfunction. One example is the Service Engine Soon light. This light is operated by the control module using a driver inside the control module. If the control module has a system failure or a system operating outside of its control parameters, it will illuminate the Service Engine Soon light. Other automotive systems will use a similar system to operate their respective lights. The anti-lock brake module may use the brake warning light and an anti-lock light to warn operators.
(Lance owned his own auto repair shop for 30 years before retiring in 2006.)