More and more vehicles are doing away with the mechanical throttle cable between the driver's foot and the engine throttle body, replacing it with a "drive-by-wire" system. In this system, a throttle pedal sensor sends data to an electronic throttle control computer, which evaluates and relays the throttle request to a specialized electronic throttle motor on the engine throttle body.
The throttle motor opens or closes the actual throttle blade, which increases or decreases the power output of the engine. The throttle control warning light illuminates when a problem is detected in the electronic throttle system.
The Bulb Check: Throttle Control Warning Light
When the engine is first started, the electronic throttle body system does a self-test. While this is occurring, the electronic throttle control system light will be lit. It is usually a yellow icon that will go out in 1 to 3 seconds if everything is normal. If the light does not go out, there is a fault condition in the electronic throttle control system.
What to Do: Throttle Control Warning Light
If the electronic throttle control light comes on during start up or while driving, then there is a fault condition developing in the system. If the vehicle still drives normally, then have the vehicle diagnosed and inspected at a qualified repair shop as soon as possible because, at some point, the vehicle may not be drivable.
If the electronic throttle control system light comes on and the throttle response becomes erratic, have the vehicle towed. It is not safe to drive a vehicle in this condition.
If the vehicle has electronic throttle control and a dead battery, do not jump-start the vehicle. The electronic throttle control light will come on after a jump start because the programming in the electronic throttle control computer can get corrupted by the high voltage and current of a jump start.
Often, the electronic throttle control light will come on after a jump start and the vehicle performance will deteriorate over time, until it becomes undrivable. When an electronic throttle control vehicle has a dead battery from say, leaving the head lights on, it is recommended to have a slow or medium charge with the key out of the ignition. This will let the computers gather their energy slowly without being shocked back to life.
The computers in a modern vehicle are somewhat active, even when the key is out and the engine is off.
Background Information: Throttle Control Warning Light
The first drive-by-wire systems were introduced to allow multiple throttle body engines, like most V12s, to have precise and coordinated throttle control. Having multiple throttle cables was less efficient and lacked precision. The need for more precision became necessary as emissions standards grew more stringent.
As manufacturers developed traction control systems, it became necessary to actively intervene with the process of opening or closing the throttle blade in the engine throttle body. When a wheel begins to slip, the engine must cut power so that the wheel can regain traction. This process needs to occur several times a second, something that is impossible for the average driver to physically do himself. Therefore, a computerized electronic throttle control system was developed to do this job.