So I left my lights on at work but my battery didn't die took a couple cranks and started right up I get on the highway and about 60 mph I'm at 3000rpm and it would not shift finally It shifted and I noticed my check engine light come on I pulled over at the gas station and cycled through it and got a code 12 and a code 55 I have no idea if that has anything to do with it not wanting to shift I checked all fluid levels they were fine my battery voltage was a little low any ideas guys? Oh and it's a 92 cherokee by the way

 

On my 98, code 12 is battery was disconnected in the last 50 start cycles and code 55 is Completion of fault code display on Check Engine lamp.

 

Code 12 means the PCM lost power (low or dead battery), 55 is the end-of-message code, just marks the end of the sequence and means nothing.
Charge up the battery and see what happens. Electronically controlled transmission's get funky with low voltage.

 

X2 on both of the above responses.

 

Any time I have ever pulled the codes from the self diagnostics, the first & last codes have ALWAYS been 12 & 55, even if the CEL wasn't on. Nothing to worry about.

 

Alternators on todays vechicles are intended to keep battery charged not recharge it from a very low voltage point .Throw a battery charger on for a few hours then drive . And all codes you read are as stated above normal.

 

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