Pontiac Repair: 2005 pontiac montana battery volts, spacer plates, pontiac montana

Question
QUESTION: The battery volts on my 2005 Pontiac Montana keep jumping up and down between 12.5 and 15.2. The dealer said it needed a new battery the alternator was replaced less than 2 yrs. ago. Put a new battery in myself, the other one was still under warranty and still having same problems. Called the dealer and they said i declined for them to put in a new battery and want to charge me again for diagnostic test. What could be the problem?

ANSWER: Hi richard:

Is this a SV6 Montana or the "old body style" Montana?


---------- FOLLOW-UP ----------

QUESTION: It's an sv6. The dealer also replaced the ignition switch assembly and the valve body, spacer plates and side gaskets in the transmission and 2 days after i got it back the car almost completely stalled and the dash said service stability control. it usually just grabs for a second. And when i was driving down the street today it grabbed briefly and said traction control active. Could this be related to anything they did?

Answer
okay. It sounds like you may have more then one issue here BUT if the battery voltage is spiking up and down the onboard control modules get stupid and can set all kinds of codes. so I wqould look at the votage issue first and it MAY fix the other things too But i doubt it.. that van had issues with the alternator. the voltage regulator would go bad and it waould cause starnge voltage outputs. the regulator is service by it's self you don't need a new alternator. That van has a top post battery make sure the cables are tight on the battery and that there is NO corrosion on either cable. either one of those should fix the voltage issue. . . . The stability light can becaused by a lot of different things like a voltage issue but other common things are ABS brake related the systems are intertwined the stability uses anti-lock brake inputs as well as a few others of it's own. with out knowing what code(S) are stored I can'r tll you what is wrong.. stop by any of the big box car parts stores and they will scan for codes for free. see what code(S) are stored and go from there. Lastly can what was done prior to this happeing cause thuis to happen? I doubt it but anything is possible. the only thing that could be related is possibly a ground wire left loose on the tranmission but without seeing it it's hard to say. Being that the van isnoiw 6 modle years old once you start digging into one system on the van it may disturb something else age takes it toll on cars and corrosion on wire connections is a huge issue and just wiggeling and jiggeling the engine to repair something can cause issues somewhere else it's just the nature of the beast. Good luck :)