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chevygeorge, ASE master tech
Category: GMC
Satisfied Customers: 53
Experience:  GM Technician for over 25 years
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2008 GMC Sierra...1st my clock would reset to 12:00 when I

Customer Question

2008 GMC Sierra...1st my clock would reset to 12:00 when I turned on my truck, then my auto door locks would click on/off/on/off, then headlights flickered. Now I was driving on freeway and engine would lose power/get it back/lose power/get it back..,
JA: Many things can cause a car to make those weird sounds. Some simple, some complicated. Fortunately, the mechanic I'm going to connect you with knows all the tricks and shortcuts. Are you hoping to fix this yourself?
Customer: Yes
JA: Great! What have you tried so far?
Customer: Nothing
JA: Is there anything else the GM Mechanic should be aware of about your GM?
Customer: No
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the GM Mechanic about your situation and then connect you two.
Submitted: 5 months ago.
Category: GMC
Expert:  chevygeorge replied 5 months ago.
Hello. My name is ***** ***** I'm here to assist you. Battery voltage issues can manifest themselves in various ways and be frustrating. I saw where you've had some issues with the battery and cable before. Is the battery in good condition? The corrosion you had before was most likely due to leaking acid. Has that been addressed? These 2007-2009's are notorious for battery cable issues very similar to what you are describing. Do you have a volt meter available were you can check the cables, preferably with clamp on leads?
Customer: replied 5 months ago.
This is a different vehicle than the one with the corrosion issue. I don't have a voltmeter but I'm going to have to get one. I am going to try changing out my battery cables 1st. I am hoping it is not the alternator and really hoping it's not my main computer. How would I check that? Would that come up as a code on a diagnostic check?
Expert:  chevygeorge replied 5 months ago.
I'm leaning towards the cables personally. There is really no way to diagnose the computer, unless you have some fault codes or it happens regularly. The way gm recommends to test the cables is with voltage drop, as a single strand of wire will have contunuity but not start the vehicle. They want you to set the voltmeter to milliamps and check the cables from end to end while cranking the vehicle with the 2 injector fuses pulled so it will not start. So positive lead at positive battery terminal and neg lead at starter, then positive at negative batttery terminal and negative lead at engine block. You should have less than 200 milliamps when cranking. Anything higher,the cable needs replaced.