Questions & Answers for: GMC Sierra 12 blinks

...key on with engine off and the codes should start to blink. All codes should start with code 12 which is one long flash followed by 2 short flashes. This code 12 means the diagnostic system is ...

...14 volts? If so,the truck is charging, so it may be time for a new battery. If the voltage is at 12 or lower while running the truck is not charging. May be time for a new alternator. The battery ...

blinks are the tens digit. EACH CODE REPEATS 3 TIMES AND THE GOES TO THE NEXT CODE SET. You will get code "12" first..."b l i n k- blink-blink" It will repeat 3 times. I bet the next code will be "32"

...and alternator, and while I'm driving the voltmeter jumps back and forth between around 12 to around 15. It's constant usually. Occasionally, it will dip to around 9, even while ...