What is an Ignition Switch?

manufacturing industry

A car's ignition switch serves several purposes. First, it allows you to control the power to many of the car's accessories, preventing accessories from running down the ca's battery when the car is parked for a long period of time. The ignition switch also serves the far greater purpose of connecting the starter to the battery, allowing the battery to send a powerful surge of electricity to the starter when the car is being started.

The term ignition switch is often used interchangeably to refer to two very different parts: the lock cylinder into which the key is inserted, and the electronic switch that sits just behind the lock cylinder. In some cars, these two parts are combined into one unit, but in other cars they remain separate. It is advisable to check your car's shop manual before attempting to purchase an ignition switch, to ensure that you buy the correct part.

In order to start a car, the engine must be turning. Therefore, in the days before ignition switches, car engines had to be turned with a crank on the front of the car in order to start them. The starter performs this same operation by turning the engine's flywheel, a large, flat disc with teeth on the outer edge. The starter has a gear that engages these teeth when it is powered, rapidly and briefly turning the flywheel, and thus the engine.

The ignition switch generally has four positions: off, accessories, on, and start. Some cars have two off positions, off and lock; one turns off the car, and the other allows the key to be removed from the ignition. When the key is turned to the accessories position, certain accessories, such as the radio, are powered; however, accessories that use too much battery power, such as window motors, remain off in order to prevent the car's battery from being drained. The accessories position uses the least amount of battery power when the engine is not running, which is why drive-in movie theaters recommend that the car be left in the accessories mode during the movie.

The on position turns on all of the car's systems, including systems such as the fuel pump, because this is the position the ignition switch remains in while the car's engine is running. The start position is spring loaded so that the ignition switch will not remain there when the key is released. When the key is inserted into the ignition switch lock cylinder and turned to the start position, the starter engages; when the key is released, it returns to the on position, cutting power to the starter. This is because the engine runs at speeds that the starter cannot match, meaning that the starter gear must be retracted once the engine is running on its own.

Either the ignition switch or the lock cylinder may fail in a car, but both circumstances have very different symptoms. When the ignition switch fails, generally the electrical wiring or the plastic housing develops problems. The car may not turn on and/or start when this happens. Also, the spring-loaded start position could malfunction, in which case the starter will not engage unless the key is manually turned back to the on position.

When the lock cylinder malfunctions, however, the operation of the key itself will become problematic. If the tumblers become stripped, the lock cylinder may be able to turn with any key, or you may be able to remove the key when the car is on. If the tumblers begin to shift, the lock cylinder may not turn. Sometimes the key can be wiggled until the lock cylinder turns, but it is important to remember that this is only a temporary fix.

Replacing an ignition switch can be tricky business, particularly in newer cars, because of the anti-theft devices used in cars. Once the ignition switch is separated from the back of the lock cylinder, the car can be started with a screwdriver, making it vital that this switch be difficult to get to. It is important to consult a shop manual before attempting this kind of repair, as the anti-theft devices may require special tools; attempting to remove an ignition switch without the proper tools can render the car inoperable.

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21
Is it true that if you have too many keys on your key ring while the key is in the ignition, that it will make the ignition go bad? If so, how many is too many? I have a 2005 yukon.
- anon50644
20
i've got a 96 caprice classic that was running fine. one day i went to start it up but it didn't start. on the dash it said pass key fault -- something to do with anti-theft. i had the key checked out. it was fine, but the battery light still comes on. what's wrong with my car.
- anon44773
19
- AngelEyesz - any answer to your issue? I have the same going on with my 97 jeep. I can start it right up and run it as long as needed, but I can't restart it for 15-30 min after that. thanks- co-apline
- anon42098
18
I asked this question and need to know if this answer is correct:

"I am having multiple issues that I think are related to the electrical system in my car. It needs to be jumped almost every time I start it, even though I have had the alternator and battery replaced. If I set the e-brake when I park, it will usually start the next time I go to start it. I notice that the fan/ac/defroster will be running 1-2 hours after I park, even while the car and the fan are both turned off. The fan will go off when I start the car. I have had it to 4-5 mechanics, with no success. A mechanic friend of mine said he though something was shorting and maybe the car had been in a flood. Any ideas?"

He responded that it could be due to water damage, but it might also be the ignition switch. After reading the above article, I'm not sure. What do you guys think?

- kwiklip
17
I have a 2002 Mustang V6. I have an interesting problem where when I turn the key to just the accessories, the car will just start up automatically. When it starts like that, I hear a grinding noise when I shift into park or neutral. Does this have to do with the ignition?
- anon38794
16
I have run into the same problem as anon28420.

My 2006 Chevy Cobalt got stuck in the ACC position. I can turn the car on but it wouldn't let me take my key out. I have the bear minimum for the features. This also means no auto locks of keyless entry. Being in a neighborhood that's not safe I can't leave the car unlocked with the key in the ignition.

I managed to get the key out. Now the tumbler is still stuck on the ACC position and I can't put in the spare key. I can turn the car on with any key. Is there a simple fix or will I need to replace the key chamber? How much does this part cost? And should I be worried about the clock being left on?

- anon33513
15
I have a 1999 ford taurus ohc. Yesterday car did not start. Got battery jumpstart 3 different times in 45 minutes by 3 different people. Car still not starting. After 30 more minutes car starts. Then in evening same thing happens. What is the reason? Please tell me. Car mechanic says "it is bad starter" Is it?.
- lewiswhit11
14
*Help!!* My Jeep Cherokee 90 is cranking but not starting! What is it? And what do I do?
- anon31116
13
Have a 1987 Chevrolet Cavalier Z24 2.8. motor initially it is starting/cranking, fine. the problems occur when the car is driven for a short or long distance. when I turn the ignition off it hesitates or won't start back up at all. i have to sit and wait for approximately 20-30 minutes b4 it starts back up. the same problem happens when the car is crunk up in stationary position. the car might start back up initially after you have driven it and turned the ignition off. if you immediately turn the ignition back on it but won't start back up if it sits for about 15-20 mins.

the car seems like when it has generated an extreme/excessive amount of heat somewhere in one of it's mechanical parts, it has to cool down b4 it starts up again, just my unprofessional guess i'm definitely not a mechanic, but I am the owner of the car for 15 yrs. Pleaseeeee ur help is very much appreciated and this is a list of things that have been replaced on the car so far:*oil pressure switch, fuel pump, fuel filter, ignition part and module.*

It was suggested that it could be the *starter motor.*

The starter motor initially cranks up fine but after it generates some heat it has to sit for about 30-35 mins b4 it starts again. My mechanic is stumped right now after replacing all the other parts. He's thinks it's not the starter motor. How can he be sure it's the starter motor when he did the basic check. What else can he do or can it be an electrical problem?

- AngelEyesz
12
Can the ignition switch cause the car to stall?
- anon28750
11
Hi, I have a 2004 Saab 9-3 Arc, and about a week and a half ago my car alarm started going off randomly throughout the night. I called the dealership and they told me to go down to O'Reilly's and get the battery checked. I did and the battery was perfectly fine. *Then* two days later, at 1 o'clock in the morning, the alarm started going off again. It did this every 2 minutes until 9 o'clock in the morning until the battery *finally* died. (I didn't know how to unhook it). Of course all my neighbors were angry and the cops came 400 times. (embarrassing, I know.)

My husband is deployed and I feel like since I am a female, all the shops I take it to want to take advantage of me. I went to the dealership, and they checked it out all weekend and at first they tried to tell me the only thing wrong with it was the battery. I flipped out and told them that the battery was checked *two days* prior and there was nothing wrong with it. And my battery wouldn't have been dead if the *alarm* wasn't going off for 8 hours straight. But anyways, they decided I needed a new ignition switch. They put that in and charged me an arm and a leg. I finally got my car back today and the alarm has not gone off not once. I am just wondering if their being an ignition switch problem sounds legit as to why my car alarm was going nuts *or* did I just get taken for 300$? *Thanks.*

- anon28506
10
*has anyone had a problem like this?*

i have a 2000 malibu and my ignition switch went bad so i got a new one, well when i hooked up the new switch and after the anti theft system went off, what it does it won't let me turn the key to the *off* position so it forces me to leave it in the ACC which leaves my radio on and my tachometer.

i tried opening doors and all that does not work. what seems to work is when i unhook the battery so that the car has no electricity and once i hook it back up it will turn to the *off* pos and that only happened once so for the second time when i started the car and turned it off it won't let me turn the key to the *off* again.

- anon28420
9
i have a 2005 Chevy Colorado 5cyl. Every once in a while i have troubles starting it. Turn the key, let go of it & it keeps on like i'm holding the key too ling. It acts like it wants to start but won't ever turn over. i can wait 10min try again & it starts like nothing was wrong. I got aggravated & crawled under the truck, tapped on the fuel lines/pump, maybe there was a block some where. I've done this the last 2 times it acted up & the truck starts right up. Just this week my gas mileage has dropped drastically. i've gone 136 miles & used a 1/2 tank of gas. That is not right for my truck. Well i took my truck to the chevy people b/c it got worse this wk. They called to let me know it's my ignition switch. Parts & labor $200. One, does this sound like a ignition switch problem? Two, does my fuel ave anything to do w/ this if it is the switch? Being female i can't help but think i'm about to be screwed! Any ideas???
- cscarecrow
8
Posted by: anon7849

i recently purchased an older vehicle (1989 nissan pathfinder) and when the starter cranks the engine starts right up. sometimes it will start on the first turn of the key and sometimes it may take 20 turns of the key to start. i'm fairly confident that it is not the starter, but the electric switch. is it more likely that it is the switch and not the starter?

- anon16301
7
Dear Stig, connect the ignition wire of the alarm to the running lights from the tow vehicle, this will set the alarm whenever the vehicle is detached and prevent the alarm from going off every time you hit a bump while towing. I would suggest mounting a solar trickle charger to the roof of your trailer and connecting it to the battery to prevent the alarm from draining out the battery, which it probably would over several weeks. Good luck with your project.
- anon15329
6
ekanayaka, you shouldn't keep the key in the "on" position because any lights, radio, guages, etc. would be run off of the battery. When the car is on and the engine is running, all of your electrical equipment is run off of the alternator. Seven minutes is no big deal though. As long as you can turn your car back on, the alternator will recharge the battery.
- anon7880
5
i recently purchased an older vehicle (1989 nissan pathfinder) and when the starter cranks the engine starts right up. sometimes it will start on the first turn of the key and sometimes it may take 20 turns of the key to start. i'm fairly confident that it is not the starter, but the electric switch. is it more likely that it is the switch and not the starter?

Mary in PA

- anon7849
4
Very useful article...thanks!
- anon6585
3
Thank you. I am having trouble with a key working in my ignition...and now I know what's going on. Thanks again!

Pauk

- anon6115
2
Why are we warned not to keep the key in the "ignition on" position when the engine is not running lest the battery be discharged and the ignition damaged? How long will it take for this to happen (minutes ? hours ?). I have a brand new Toyota Yaris and today I switched to the "on" position when parked to pull down the electrically operated windows and forgot to switch off for about 7 minutes!! Should I worry ??? - Please reassure if possible !

Dr. Asoka Ekanayaka

- ekanayaka
1
if i was to install a car alarm on my trailer which has no engine, only a 12-volt battery... where would i connect the ignition wire lead of the alarm?
- stig

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Written by Katharine Swan
Last Modified: 22 November 2009

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