The ignition switch, located on the steering column or in the dashboard, takes the power from the battery and directs it to all the accessories and electrical components of your car. It also transfers the power to the starter when you turn the ignition key.
An ignition switch has four positions which transforms into making a car to move:
OFF Or LOCK position; Turns off power to the engine and electrical accessories
ACC – Accessory position that provides power to electrical accessories only, not the engine.
RUN – The “ON” position that provides power to the engine and electrical accessories. The switch must be in this position for the engine to run and for the vehicle to be driven.
START – Used only to start the engine.
IGNITION SWITCH ANTI-THEFT FUNCTIONS
The ignition switch also serves as a theft prevention device. A key is required to turn the switch. The key portion of the switch (which is often a separate component from the multi-contact electrical part of the switch) works like any other lock. Inserting a key into the switch moves a row of pins inside a cylinder. If the pins line up correctly, the cylinder will turn allowing the switch to change position. If the pins don’t line up, they prevent the switch from turning. Problems here can be caused by a worn key and/or worn pins inside the cylinder.
On applications where the electrical part of the switch is a separate component behind the key cylinder, removing the key cylinder allows the switch to be turned manually (typically with a large screwdriver). On older vehicles, car thieves would use a slide hammer or pry bar to pop the key cylinder out of the ignition switch so they could start the engine without a key. But all that changed when auto makers began using anti-theft systems that included a coded “computer” key.
On newer cars, the engine won’t start even if the key cylinder has been removed because the computer must receive the proper code from the key. If the vehicle has a push button start system (no key), the anti-theft code comes from the key fob. If there’s no code (or the wrong code), the computer won’t energize the fuel pump or start the engine — and the thief can’t steal the car. Starting problems here can occur if the circuit that reads the smart key or key fob is faulty and doesn’t recognize or transmit the proper signal back to the computer. The same thing can happen if the smart key or key fob is defective or damaged.
On some applications, the anti-theft system can be confused if there are more than one smart key on the key ring and the system is reading the wrong key. This may happen is the second or third keys are for a similar make/model of vehicle rather than a different make/model of vehicle.
IGNITION SWITCH INTERLOCKS
The ignition switch is also used to lock the steering wheel when the key is removed. This is also to reduce auto theft. On vehicles with automatic transmissions, there is also a “shift interlock” solenoid that locks the transmission linkage so the transmission cannot be shifted out of Park.
Problems with the column lock (such as binding) may prevent the ignition switch from turning when the key is inserted, or it may prevent the key from being removed when you turn the engine off.
Problems with the shift interlock solenoid may prevent the transmission from being shifted out of Park. The cause may be a bad solenoid, an electrical fault between the ignition switch circuit and the interlock solenoid, or binding in the shift interlock linkage. In the next post we will be addressing the common ignition switch problems and some recommended solutions for the problem.