I have a 2005 Pontiac Rally Aztec. I just got a new battery Sunday because I keep having to charge my battery every morning and afternoon after it sits for a period of time. What is causing this? I had the alternator check and it was good. Need help ASAP...

Better to do that with a high end scan tool. You can't do it by disconnecting the battery overnight, but that can cause all sort of new problems. Where you say your speedometer 'sets' at 55mph, do you mean always stays at 55 even stopped, or do you mean if 'sits' at 55 even if you are doing 110?

The most likely cause of all this the VSS (vehicle speed sensor)

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To keep them running, pull the plug off the engine coolant sensor. They will run even with the key on (PCM default). To get them to stop running, replace the engine coolant sensor.

Aztec was derived from the line of GM minivans. Many mechanical parts are interchangeable with Pontiac Montana, Chevy Venture and Olds Silhouette of that vintage. Obviously the sheetmetal is, I would say, unique.

Check out and watch starter motor trouble shooting tips DIY on YouTube. This should be a good guide to help find your problem.

look up pontiac recalls,They had a problem with some type of relay in the ignition recalled back in 2005.free fix for you at dealership!!! Hope this helps!!

Not really following your story.
When you say it will not start, the starter would only affect things if the engine will not crank.
If the engine will not crank, you would need to know if the battery is fully charged and if the starter has power and ground.
If the battery is low, something may be draining it overnight. If the battery is charged, the starter should have power.
The neutral safety switch or key switch could be the problem if the small wire on the starter has no power when the key switch is in the start position.

need to see if its a seal or gasket

have you checked / changed radiator? check for water flow?

a bad conection on battery clean both cables

Try resetting the alternator, if that doesn't work try changing the battery

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