An ignition switch or a start switch is a mechanical device that is used to activate different electrical circuits of a vehicle. Which one is activated at the moment depends on the position of the ignition key in the switch. As a general rule, a typical switch features four main positions, including lock, accessory, run and start.
Lock or off ignition switch position
As its name indicates, the lock (off) position cuts all electrical circuits powered via the ignition switch. Plus, it blocks the mechanism of the steering wheel to protect your vehicle from car thieves. This is the default ignition switch position which allows the driver to insert or remove the ignition key. On vehicles equipped with an automatic transmission, the off position also locks the gear selector.
Accessory ignition switch position
The ignition key in this position activates an electrical circuit that powers the radio, lights and some other accessories. However, the starter circuit and engine control circuits remain deactivated.
When you set the ignition switch into the run position, you engage all electronic devices and engine control systems that are powered through the switch, except for the starter.
This ignition switch position completes the starter circuit, powering the starter, so it can crank the engine. It also allows the engine control unit to prepare your vehicle for operation.
Your ignition switch is manually operated with your ignition key. You should insert the key into the lock cylinder when the switch is in the lock position and then rotate it to choose the desired position. Keep in mind that leaving the ignition key in some positions for a long time can deplete the battery because the alternator is not involved. Thus, listening to the radio with the key in the accessory position will do that quickly.
In addition to its primary function, your ignition switch serves to prevent the vehicle from getting stolen. Thanks to the fact that it can be operated only by a unique ignition key, nobody will be able to run the accessories or to start the engine without the key. The ignition key must be inserted into the lock position to unlock the steering wheel and the gear selector.
While an ignition switch has proven its efficiency over the years, most modern vehicles today come with a start button instead of an ignition switch. When the start button is pushed, the vehicle’s computer understands that you are ready to drive. It checks the position of the gear selector and the brake pedal to make sure the selector is in park and the brakes are engaged. If everything is fine, the computer involves the starter to crank the engine.
The ignition switch is a crucial component of your vehicle’s ignition system. Its failure will cause a number of ignition related problems:
Your engine stalls
Burnt or worn-out switch contacts can restrict current flow to the engine control system, which may cause your engine to stall. If this happens on the go, your vehicle may cause an accident.
You can’t start the engine
Your starter, engine control system and ignition control system are powered by the ignition switch. Its failure will cut their power circuits, so your engine won’t start.
Flickering dashboard lights and accessories
This is a sign of bad ignition switch contacts. They disrupt power supply to the accessories and lights, causing them to blink or stop working suddenly.
It’s difficult to remove the key
A worn out or damaged ignition switch can get locked in an incorrect position, making it difficult or impossible to remove the key. In some cases, the engine can continue running while the key is off.
Ignition switch troubleshooting
Several symptoms caused by other ignition components like an ignition key or cylinder lock can be misinterpreted as signs of a bad switch. We recommend you to provide a thorough diagnosis of the ignition assembly before replacing the switch. In some cases, you’ll just need to replace the lock cylinder or the ignition switch or even use another ignition key.
You can prolong the service life of the ignition switch and the lock cylinder if you avoid using heavy keychains. We recommend you to use the ignition key separately without any other keys attached to the chain.
Unless you’re a mechanic, replacing a bad ignition switch should be left to a professional. In many cases the replacement process involves disassembling the steering column and deactivating the airbag.
Any symptom of a faulty ignition switch should be addressed once it appears. Driving a vehicle with a bad switch can put your life at risk and affect your vehicle’s drivability. It’s better to have your vehicle towed to a repair facility.