Mechanics

Ignition Switch

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Ignition Switch with Key
Ignition Switch

Once you are all buckled up, mirrors adjusted and ready to go, the next step is to start the vehicle, this all begins with the ignition switch. Where you insert the key is not actually the ignition switch, it is called the tumbler assembly, and the electrical switch is a separate piece. In this article we will explain the difference, and hopefully answer any questions you may have about the switch-tumbler assembly. The key tumbler is where the security aspect comes into play. An automotive ignition key tumbler works just like any other tumbler assembly, the key pushes up a particular set of pins allowing the key to turn and activate the electrical system. Some automotive key tumblers integrate extra security measures in the form of chip coded keys that are read by a sensor in the tumbler assembly.

These keys provide an added layer of security against theft by shutting the computer or particular vital systems (fuel pump, ignition system) down unless the proper key is inserted into the tumbler. These keys have to be copied by a special machine that programs the chips. Some manufacturers combine the tumbler and switch assemblies into one piece, these styles are usually the dash mounted type of ignitions while the column mounted ones use a rod and rack assembly to activate the electrical switch which is mounted on top of the steering column under the dash. Newer vehicles have pretty much abandoned the lower column mount switch in favor a multi service turn signal switch that is mounted directly behind the tumbler assembly on the upper column. This design eliminates several moving parts for added durability and easier replacement.

The ignition switch is what powers up the key components of your vehicle, from the computer PCM (Powertrain Control Module) to the BCM (Body Control Module), and in some cases the TCM (Transmission Control Module). The starter or starter relay gets its trigger signal from the ignition switch as well. When the ignition switch has an issue it can cause a wide variety of symptoms. When you consider how many things it controls the power of, it is no surprise that this one switch can cause a transmission to not shift or the vehicle to simply not start. As the ignition switch in your vehicle gets older, the contacts inside it can become corroded or dirty causing poor continuity, this can cause the vehicle to crank hard or possibly even set faulty trouble codes in the control modules due to low circuit voltage.

If it has been determined that the ignition switch in your vehicle needs to be replaced (electrical) you should consult an automotive repair manual for any special procedures that need to be taken to ensure a proper repair and no injuries to the person working on it. As far as replacing the tumbler assembly, the steering wheel needs to be removed (Column mount ignition), this may require disarming and disabling of the SRS (Airbag system), and for this you will also need to consult a service manual for the proper procedure, otherwise serious injury could occur. For replacement of dash mounted assemblies, the SRS system may not need to be disarmed, but you should consult a repair manual to verify that for your particular vehicle. Regardless of which type of switch your vehicle has, you should always use OEM (Original Equipment Manufacturer) parts or the equivalent. Cheaper electrical parts tend to use lower quality materials in the contacts which can cause them to be unreliable and not last as long as the higher quality parts.

If further technical assistance is needed, ask our team of certified car repair technicians.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-21)