Engine/Transmission (1994 - 1998) codes since alt. change

[edmeyers]

i changed my alt. because it was not charging (bought one from autozone) and now it shows it is charging but m check engine light comes on with these codes in this order 12 41 11 47 34 55 i am aware of the 55 being at the end but i since i changed th alt i have started it at lease 50 times so i don't know what the 12 is all about. also my speedo does not work until the truck gets warm (i know that does not make sense, but that is what happens) so i believe the 34 is set by that. now my question is what is setting the 47 and 41 i had a 41 before i changed the alt. but it has not gone away. all this does not seem to affect the way the truck drives it's just annoying seeing the check engine light come on. please help me on thi i am stumped

 

[Sageair]

It sounds to me like the voltage regulator in the alternator is not right. If you have access to a voltmeter/multimeter check tne battery voltage with the truck running. Float voltage should be between 13. 8 volts and 14. 2 volts DC. Be sure to give it a few minutes after starting for the grid heaters to turn off.