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Festival
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275 Posts
Discussion Starter #1
I have a 2004 GMC Sierra 1500, I recently had an issue where the truck didn't crank over in the parking lot, and I let off the key and tried starting it again, and there was no response at all.

I waited 15 seconds and cranked it again and it fired up, but I got the DIC error message about "service brake system" along with ABS & Park Brake light on dash. When I got home, I decided to take my battery in for a test, so I unhooked it and went to Partsource. Battery charge ended up being low and the CCA was only 270 (rated for 600). Took it home and left it on my trickle charger for 6 or so hours, took it to get tested again and they say it was fine, actually showing 700 CCA which was rated over the 600 CCA for the battery.

Reinstalled the battery, and now I feel like my idle is low. When I am stopped at a light, I can see the tach around 500 RPM, and the needle shudders slightly as well. The first drive after putting battery back in, I was at a light and the RPM dropped to probably ~400, entire truck began to shudder. I quickly turned off the radio/heater and the RPM came back up to 500 and shuddering stopped. Took off and it continues to read around 500 rpm at idle.

Any thoughts? I don't want the truck to stall out on me randomly. Never had this issue before! Is the battery maybe f****, even though the battery tests say it's fine?
 

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645 Posts
Test your alternator, if the diode pack is going bad it will do very strange things like this.
 

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Festival
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275 Posts
Discussion Starter #3
Sure, I can try it out. Voltmeter in the dash always shows 14V though..I guess it could be nonfunctional though.
 

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The problem with using the gauge is that the diodes being bad will cause AC pulses instead of DC pulses and it can happen faster than the gauge can react. You will want to remove the alternator and take it down to get tested, I don't think testing it on the vehicle will be good enough. Also, if you buy an alternator at a Autozone or Orielly's or something, have them test the new one before you leave. It's annoying when you get home with a defective alternator...It's happened to me twice.
 

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Festival
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275 Posts
Discussion Starter #5
Shoot. Thanks for the input. I'll see what I can do.
 
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