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Ryan Schott
Ryan Schott,
Category: GMC
Satisfied Customers: 82
Experience:  technician at Demarois Buick Gmc
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I have a 2002 GMC sierra 1500 (5.3L) and am having power

Customer Question

Hi, i have a 2002 GMC sierra 1500 (5.3L) and am having power issues (the battery and alternator have been replaced less than a year ago) My battery is between 12v-13v when off and 14v when running (with accessories on). When im driving and i use the turn signals the battery gauge ticks in tune with the blinker, if i have the radio, and heater on my power will spike low and go back up. One morning it sputtered and lights were dim, but giving gas brightened them up and stopped the sputtering. However on three other occasions my heat and radio quit , all the dash lights came on and giving gas made the issue worse, pulling over, shutting off my truck and restarting fixed it for each of the times.
Submitted: 7 months ago.
Category: GMC
Expert:  Ryan Schott replied 7 months ago.

Three things that will commonly cause this, a bad ground, excessive voltage drop in cables, or an ignition switch. the ignition switch can usually be checked by when it occurs bang on your steering column and see i it goes away. voltage drop you need a voltmeter to check, putting it to DC volts hook one lead to one end of A battery cable and the other to the other end o the same cable, then crank the engine and watch what it spiked up to, .2v is a fail. do this to all battery cables, negative, positive to starter, and positive to fuse block. while doing the negative check the engine ground and follow the small lead down to the frame and check its ground. also check the ground to the back of your driver side cylinder head. let me know what you find

Customer: replied 7 months ago.
i did the tests on the positive i did the cable at the post to the fuse box and got 0.019V (DC) and between cable at the post to starter and got the same. On the negative side i tested from cables at the post to the ground at the top of the hood and got 0.010V, than cable at post to end of cable on engine and got 0.007V, and the small lead from negative post to end on frame and got 0.016V.
Customer: replied 7 months ago.
also a side not i scrapped through the dirt to make sure i had a good connection for each one.
Expert:  Ryan Schott replied 7 months ago.

is it relatively easy to duplicate the condition as far as devices turning off? i would remove the column cover behind the steering wheel and expose that ignition switch so you can tap it if devices start going haywire and see if it goes away, also good to check there for any aftermarket devices wired to ignition in that harness.

Customer: replied 7 months ago.
ive never tried to force it, i have been keeping keeping everything off for the past few days haha not so fun without heat in the winter but i will go turn everything on and try it right now.
Customer: replied 7 months ago.
i haven't had any spikes yet and they typically happen fast when they do so im thinking i cant force it, but the battery gauge in the truck is slowly dropping. was exactly in between 14 and 19 and now its on 14.
Expert:  Ryan Schott replied 7 months ago.

thats normal as it has to charge higher after startup to replenish, if you can get someone to check codes that can help but no worries if not, and a good battery tester would not hurt because a bad cell will do bizare things and i have seen brand new batteries fail before. i would first try and duplicate it though and tap on that ignition switch, also if that does nothing before you restart it try unplugging the alternator electrical connector while running. but lets see if we can duplicate it and start there.

Customer: replied 7 months ago.
I do have a scanner (innova 3130c) if that would help but the only thing that I have coming up with that if is a fuel level sensor issue. I have a new float and sensor I'm just waiting for summer to put it in.
Expert:  Ryan Schott replied 7 months ago.

good i just wanted to see if there were any u-codes present. looks like we are okay there. since the problem seems to be under higher load IE your lights etc were on lets try that voltage drop test again under heavy load,remove the inj1 and inj2 fuses from the underhood fuse block then hook up your meter again and crank away on it, this way it will not start and the starter will be putting a high load on the cables and we will have more accurate readings

Expert:  Ryan Schott replied 7 months ago.

you will have to try and stick your meter where you can see it while cranking.

Customer: replied 7 months ago.
I'm on call today and I just got called. Is it alright if I get those numbers to you tomorrow? I can finish off and rate today if you want but I won't be able to test right now.
Expert:  Ryan Schott replied 7 months ago.

no problem

Expert:  Ryan Schott replied 7 months ago.

the other location ive seen a lot of water issues is the IP fuseblock, behind the glovebox on the far right, I would remove it completely open it and dry everything clean it all, blow out the connectors with air and put dielectric grease on everything one sec and ill get you the procedure and some pictures

Expert:  Ryan Schott replied 7 months ago.

sorry wrong post ignore that last one