Believe it or not, this is related to a rash of bad ignition switches in GM vehicles. When the switch fails in the open position, it doesn’t provide battery power to the Brake Transmission Shift Interlock (BTSI) fuse. The BTSI system consists of the brake pedal switch and a solenoid on the shifting mechanism. The BTSI prevents you from shifting into and out of park unless your foot is pressing on the brake pedal.
Unfortunately, when the ignition switch fails, the BTSI system also prevents you from completely shifting into park and removing the key. To confirm that this is the cause of the problem, check for battery voltage at the BTSI fuse in the fuse box with the ignition turned OFF. If you don’t get voltage at the fuse, move to the ignition switch. Check for battery voltage at the B+ terminal. It should read within 1 volt of battery voltage. If not, replace the ignition switch
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© 2012 Rick MuscoplatPosted on by Rick Muscoplat