One morning I slid behind the wheel of my Jeep, slid the key into the ignition, and tried to start the engine. I was met with the ominous clicking indicating a low battery. And, the dash was ablaze with a series of warning lights.
First step, get the engine started. I carry an emergency battery pack that provides the necessary power to start a vehicle engine. Within minutes, the engine was started and running very rough. The dash warning lights were reduced to two, the Electronic Throttle Control warning and the Check Engine Light.
The ETC warning was a simple fix with a few key clicks and timed pressing the throttle pedal. While that warning light was quickly cleared, the Check Engine Light remained on and idle remained very rough.
My INNOVA 5310 code reader revealed a stored trouble code - P-0300. By definition, that code indicates multiple random mis-fires. The list of possible causes was long, some easy and some not so easy. A series of repairs were in order, starting with a new battery and tuneup.
Read more at: http://www.4x4wire.com/entry/jk-check-engine-light-p0300