Use your foot to hold the brake pedal up. If it sets, the switch is out of adjustment or the contacts for the cruise control circuit are pitted.
If that doesn't help, the fastest way to diagnose it is to connect the Chrysler DRB3 scanner. It will display "Reason for last cutout". It will list "ignition switch turned off". Duh. Naturally it can't work when the engine is off but the point is if that came up while you were driving on the highway, you would look in the power circuit for an intermittent connection. If you left the engine running when you got to the shop, the reason listed would be "speed below minimum threshold", (35 mph) or "brake pedal depressed". If those popped up while driving, the suspects would be a defective speed sensor or a problem with the brake light switch.
There can also be a problem with the servo. There are three solenoids in it and the Engine Computer can detect when one of them is open. It will set a diagnostic fault code in memory, but those codes won't turn on the Check Engine light because the problem won't affect tail pipe emissions. The DRB3 will also show switch state. It will display the position of the brake light switch, ignition switch, and cruise control switches.
Monday, January 24th, 2011 AT 2:20 AM