Alarm Systems Triggering Misfire Codes
GM has determined that aftermarket alarm systems that use mechanical relays wired into the ignition system can generate actual ignition misfires that are serious enough to damage the catalytic converter. Mechanical relays have contact points mounted on a spring. Vehicle movement, pot holes, bumps, etc., can jolt the contacts enough to interrupt the ignition circuit for a few milliseconds. That’s enough time to cause a misfire. The unburned fuel from that misfire causes overheating in the catalytic converter and if the misfire continues, can actually cause a meltdown of the precious metals inside the converter.
GM’s research of common aftermarket alarm system found that all used a mechanical relay. The use of a solid state relay could eliminate the problem. Until the alarm manufacturers re-design their system, installers and do it yourself vehicle owners should avoid connecting the alarm system to the ignition circuit. They should instead use the starter circuit.
GM has also advised their dealers of this problem and if your car is showing any of these misfire codes, P0300, P1380, or P01381, you should try disconnecting your alarm system before taking the vehicle into the dealer. If the misfire and converter codes continue, then you can at least rule out the alarm system. Otherwise, the dealer may charge you for diagnostics related to your alarm system.
For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.
If you just need information for a single repair and want to save money,eautorepair offers a lower price 1-week subscription for only $11.99. Or, if you’ll be working on this vehicle in the future, you can buy a 1-year subscription (Alldatadiy.com for $26.99, or eautorepair.net $29.99)
© 2012 Rick Muscoplat
Alldata and Eautorepair are both professional grade shop manuals. You’ll find more in-depth information and more complete wiring diagrams, along with descriptions of how the systems work. And, you’ll get all that at a price you can afford. Check them out!
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