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Discussion Starter · #1 ·
Any ideas? Cleared codes unhooked battery for 15 minutes, drove fine, shifted fine for about a mile, then back to lights flashing on the dash, speedo and tach going ape ****, abs light, brake light, traction off, and contact dealer flashing like crazy and stuck in second gear again. Code u0121 and p0856 but u0121 can Right back after clearing codes. when the car is off and key in the ON position the abs, traction control and brake light keep coming on and off then after awhile stays on.
 

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Have you checked and or replaced the Alternator? Bad voltage can give you lots of electrical issues like you mentioned.
 

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Discussion Starter · #4 ·
Have you checked and or replaced the Alternator? Bad voltage can give you lots of electrical issues like you mentioned.

I was think that but the abs, traction and brake light comes on and off with car in on position. With the car on I do hear a whine but someone mention it could be because of (whatever the problem is causing the drops) making the alternator whine. All engine bay and truck ground looks good to me.
 

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Discussion Starter · #5 ·
Have you checked and or replaced the Alternator? Bad voltage can give you lots of electrical issues like you mentioned.
I was thinking that but the abs, traction and brake light comes on and off with car in on position. With the car on I do hear a whine but someone mention it could be because of (whatever the problem is causing the drops) making the alternator whine. All engine bay and truck ground looks good to me
 

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You can check the voltage while running, put it Engineering mode and see what it does, see if it's erratically changing or high/low.
 

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Discussion Starter · #8 ·
Been messing with it all day. now the brake light and abs light stays on all the time unlike before where it was on and off. I unplugged the ebcm harness and the contact dealer light stayed on still have u0121. some odd reason 3 more codes popped up which triggered the cel but went off
 

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Pinched wire somewhere causing issues, had something worked on on the car recently?
 

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Did the codes appear suddenly?
 

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Discussion Starter · #11 ·
nope.....curious I used hp tuners to check codes. I decided to scan the car while it idle. then It just lost connection. car was running but scan showed nothing the froze. Now I can't connect the car anymore. I'm guessing a bcm issue.
 

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Discussion Starter · #12 ·
Did the codes appear suddenly?
yes. so basically when it first happened abs light, brake and traction control would come on, cut off for like 5min then when it came back on the contact dealer light would flash for half a sec, gauges go up and down. I also hear the door lock as well. next the lights started goin on and off while I'm just sitting with the car off..Now to the tc, abs and brake light stay on. I did get a coolant sensor code and throttle body codes out of nowhere but never can back when I deleted it.
 

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Discussion Starter · #13 ·
nope.....curious I used hp tuners to check codes. I decided to scan the car while it idle. then It just lost connection. car was running but scan showed nothing the froze. Now I can't connect the car anymore. I'm guessing a bcm issue.
alternator is making a whine now but that could because by whatever is making the car surge.
 

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Anything plugged into the on-board dianostic box? Is the onstar box connected?
 

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If something is plugged into the on-board diagnostic port remove it. Correct, the OnStar box is on the left. Disconnect it unless you're an Onstar subscriber. Heck, disconnected both the OnStar and XM radio satellite boxes as well as the OnStar backup battery soon after the free subscription expired.
 

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Discussion Starter · #17 ·
If something is plugged into the on-board diagnostic port remove it. Correct, the OnStar box is on the left. Disconnect it unless you're an Onstar subscriber. Heck, disconnected both the OnStar and XM radio satellite boxes as well as the OnStar backup battery soon after the free subscription expired.
Will disconnect when I get home. the first two codes I got was u121 amd p0856. after clearing codes only u0121 stayed. while taking panels off to get access to the bcm check engine light came on for a sec. codes were u0121, p0118, p0122, p0223.
 

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Discussion Starter · #18 ·
Another thing when I check to codes when the CEL pop up It said no codes found. I had to go to pontiac enhanced codes(which I believe it shows you codes that doesn't trigger the CEL) to find it. Plus monitor only showed CCM. even if it's not ready it will still show misfire, 02 sensors, evap ect.....
 

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Discussion Starter · #19 ·
If something is plugged into the on-board diagnostic port remove it. Correct, the OnStar box is on the left. Disconnect it unless you're an Onstar subscriber. Heck, disconnected both the OnStar and XM radio satellite boxes as well as the OnStar backup battery soon after the free subscription expired.
unplugged both connections from the OnStar. nothing on the cluster moves(gauges) and contact dealer stays on.
 

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Recall a member wrote unplugging the OnStar box remedied similar issues and hence the notion.
 
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