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Discussion Starter #1
I have a 2010 LMM , Alternator was bad so i changed it from a bosch 125amp to a AC Delco 160amp, parts guys said it would be fine. Drove it out of my shop and the engine light came on. Found a ton of random codes. Cleared them and drove it about a week then same isssue. Now it seems to be stuck in 4th. i have recently replaced the TCM and ECM . Wondering if i should switch back to a stock alternator, if the higher amps would cause this ? Thanks Will
 

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I have a 2010 LMM , Alternator was bad so i changed it from a bosch 125amp to a AC Delco 160amp, parts guys said it would be fine. Drove it out of my shop and the engine light came on. Found a ton of random codes. Cleared them and drove it about a week then same isssue. Now it seems to be stuck in 4th. i have recently replaced the TCM and ECM . Wondering if i should switch back to a stock alternator, if the higher amps would cause this ? Thanks Will
Unless the alternator had the wrong sized pulley and was getting under driven (parts guy screwed up and gave you the wrong one or something) the alternator is not your issue. You could put a 500A alternator on there and it would no hurt anything. The alternator will only put out what is needed for the truck. The current rating on the alternator is a maximum not a constant. Were the alternator under driven, it would not create enough power, and low voltage issues are basically what GM does for a living.
 

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J83 is always right on the money with his analysis. 500 amp alternator should work fine, as long as it is properly connected and working correctly.

It is always disappointing and confusing when you change some simple part like the alternator and you get crazy results like you did. I hope you did not short anything out and made the alternator change with the key off and batteries disconnected. You might want to remove and then re-insert the electrical connector going into the alternator to make sure you have good contact. Good, tight, clean electrical connections are a must for the system to work correctly. Corrosion or increased resistance in an electrical circuit can cause a variety of problems.

I would clear the codes now existing and then see what happens, recording the new codes. Perhaps with the codes that are set, we might be able to have a chance to see if there is something that looks like a common thread and a possible solution.
 

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Just went to the parts store and load tested batteries. Both batteries passed but one was on the low end of passing. Napa replaced batteries free of charge and cleared codes. So far 100 miles under new batts and same 160amp alternator and no engine light. Will update if any changes. You guys rock duramaxforum.com and clients are a big money saver I'm hooked. Thanks Again.

Will
 

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Just went to the parts store and load tested batteries. Both batteries passed but one was on the low end of passing. Napa replaced batteries free of charge and cleared codes. So far 100 miles under new batts and same 160amp alternator and no engine light. Will update if any changes. You guys rock duramaxforum.com and clients are a big money saver I'm hooked. Thanks Again.

Will
old batteries will cause lots and lots of weird, intermittent and hard to trace problems on our trucks. the charging system is the first place i send people to look for solutions to any bizarre issue that cant be easily explained by other problems.
 
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