How to Disable Ignition Security in a GMby Mark Robinson
Most GM vehicles come with the Passlock II ignition security system, an anti-theft device that disables the vehicle's ignition system during most theft attempts. The most common failure mode of Passlock II is when the ignition switch no longer recognizes the resistor embedded into the key, causing a no-start condition. You can permanently disable the system, but it takes a bit of work to do so and it removes a significant amount of protection against vehicle theft.
Pull the hood release lever on the left side of the driver's side foot well and pull the hood release latch upward to raise the hood. Disconnect the negative terminal cable from the battery.
Apply the parking brake and move the shifter out of the way of the bezel. Use a flat-head screwdriver to pry away the bezel from around the radio. Pull the bezel away from the radio area and set it aside. Remove the three mounting bolts from the radio with a ratchet and socket. Pull the radio out of position, but do not disconnect the large power connector from the back of the unit.
Look through the cavity to the left of the radio opening and locate a bundle of wires wrapped in black fabric tape. These wires go to the ignition switch. Use a flashlight for greater visibility. Look for the black, white and yellow wires entering this wiring harness from a separate connector near the ignition switch.
Isolate the three wires and cut through the yellow wire with a wire cutter, leaving the end of the wire leading into the bundle as long as possible. Strip ½ inch of insulation from the end of the yellow wire where it goes into the bundle. Do not cut the black wire. Strip ¾ inch of insulation from the black wire without cutting it in half.
Wrap one of the resistor leads around the exposed black wire and cut off any excess lead. Use a soldering iron to apply enough solder to connect the lead to the wire. Slide a length of heat shrink tubing over the yellow wire. Wrap the other end of the resistor around the exposed yellow wire and secure it with solder.
Test the modification before reassembly. Reconnect the battery, insert the key into the ignition and start the vehicle. The vehicle should start, and then stall while the SECURITY light flashes. Leave the key at the ON position for 10 minutes and wait for the SECURITY light to go away. Turn the key to the OFF position for 5 seconds and restart the car. The car should start and the SECURITY light should remain off.
Disconnect the battery once more and slide the heat shrink tubing over the resistor and exposed wiring. Use a hair dryer to shrink the tubing. Apply black electrical tape to the other end of the resistor. Place the wiring back into the cavity.
Reconnect the antenna wire into the radio and place the radio back into its mounting area. Reattach the three mounting bolts and tighten them with the ratchet and socket. Reattach the bezel over the radio and move the shifter back into position. Disengage the parking brake. Reconnect the negative terminal cable to the battery and close the hood.
Things You'll Need
- Ratchet and socket set
- Flat-head screwdriver
- Black electrical tape
- Heat shrink tubing
- Wire cutter
- Soldering iron
- Resistor, 1,500 to 3,300 ohms
- Hair dryer
- Always disconnect the battery when working on electrical components. Doing so will reduce the likelihood of shock and serious injury.
Mark Robinson is a freelance graphic designer and writer. Since 2008 he has contributed to various online publications, specializing in topics concerning automotive repair, graphic design and computer technology. Robinson holds a Bachelor of Science in graphic design from Alabama A&M University.