12 Battery or computer recently disconnected (will occur on most cars most of the time, it indicates a low / missing battery happened in the last 50 key starts.)
55 is end of message. If that is the only code you have, then there isn't a problem
Codes on a 1995 Jeep are two digits long. So 5 means nothing.
Diagnostic Code 12 on a 1995 Grand Cherokee just means that your battery has been dead or disconnected within the last 50 ignition cycles.
Diagnostic code 43 in the 1997 Jeep Grand Cherokee refers to an issue with the distributor. This often causes the Jeep to stall at operating temperature.
All codes for a 2004 jeep grand Cherokee would be four digits prefaced by a p for powertrain codes, a c for chassis codes, and a b for body codes. On a 1995 and before jeep a code 15 was a vehicle speed sensor failure.
Throttle position sensor out of range.
Cylinder #1 misfire.
catalytic converter circuit
23
Map sensor voltage low.
Engine speed sensor circuit malfuntion
Trouble code P1762 means: Governor pressure sensor offset improper voltage