GMC

GMC Troubleshooting Questions? Ask a Mechanic for Answers

Ask an Expert,
Get an Answer ASAP!

GMC

I bought a used 2009 gmc seirra sle 4x4 and shortly after

Customer Question
the volt meter would slowly...
I bought a used 2009 gmc seirra sle 4x4 and shortly after the volt meter would slowly drop to 12 volts and comes back up after a while. the trans starts slam shifting and the cruise stop working, then the other night the lights started flashing and door locks started cycling and speedometer started bouncing. pulled over and stopped and restarted and worked ok the rest of the night. whats up?
Submitted: 1 year ago.Category: GMC
Show More
Show Less
Ask Your Own GMC Question
Answered in 50 minutes by:
12/31/2015
GMC Mechanic: Tim Mohr, ASE MASTER TECH replied 1 year ago
Tim Mohr
Tim Mohr, ASE MASTER TECH
Category: GMC
Satisfied Customers: 16,101
Experience: 30 YRS EXPERIANCE, AUTO AND TRUCK,FOREIGN AND DOMESTIC, GAS AND DIESEL
Verified

Hi, my name is ***** ***** you installed the new alternator, you said it dropped down to 13 volts, but did the light flash and the transmission slam still, or just the voltage drops?

Ask Your Own GMC Question
Customer reply replied 1 year ago
I did not drive, just put old alt back on. when it does this you can rrestart and volts come back. the lights and door locks was new. the trans only does the hard shift occassionally and get check engine light sometimes when volts drop. the code was like 700 something which is trans problem. I also am a master mechanic and have been building cars since the 60's and have a very good expertise with electronic repairs
Customer reply replied 1 year ago
a gm service manager told me that there is a problem with dash units on some of these trucks
GMC Mechanic: Tim Mohr, ASE MASTER TECH replied 1 year ago

This vehicle uses an Electrical Power Management (EPM) for the charging system. This system monitors electrical items such the state of the battery, vehicle electrical draw and driving conditions. . If the EPM system selects a "Fuel Economy Mode", the battery voltage will drop to about 12.5 volts until another mode is needed. So it is likey the old alternator was bad, so I would reinstall the new alternator and see if the driving problems are gone npw, it is normal operation for this system to drop the voltage, as long as it does not go below 12 volts,Tim

Ask Your Own GMC Question
Customer reply replied 1 year ago
dont buy that. my son has exact same truck only 08 and his has never done this. the trans is intermitent and the door lock and flashing light and dash module has only done this once. thanks anyway i'm going to unload this pos
GMC Mechanic: Tim Mohr, ASE MASTER TECH replied 1 year ago

this comes straight from the GM manual , you dont have to buy it, but it is the truth,Tim

1. This vehicle uses an Electrical Power Management (EPM) for the charging system.

2. This system monitors electrical items such the state of the battery, vehicle electrical draw and driving conditions.

3. If the EPM system selects a "Fuel Economy Mode", the battery voltage will drop to about 12.5 volts until another mode is needed.

4. Check for charging system related codes in the Body Control Module (BCM), and Engine Control Module (ECM). Verify the battery tests good and all wiring is in good condition.

5. If all OK, this is a normal condition.

Ask Your Own GMC Question
Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1,696
1,696 Satisfied Customers
Experience: GM Grand Master Technician 2007. 14 year experience.

Gm Tech (Cam) is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here.

DianeDallas, TX

< Previous | Next >

Meet the Experts:

Gm Tech (Cam)

Gm Tech (Cam)

GMC Mechanic

1,696 satisfied customers

GM Grand Master Technician 2007. 14 year experience.

Gary

Gary

ASE Certified Technician

1,552 satisfied customers

GCM master tech over 25 years

Dave Nova

Dave Nova

GMC Technician

929 satisfied customers

ASE Master Certification. GM World Class Certification

Chris (aka-Moose)

Chris (aka-Moose)

GMC Technician

576 satisfied customers

16 years of experience

Ron Z.

Ron Z.

- GMC Tech -

259 satisfied customers

18+yrs experience. State Inspector & GMC Diagnostics/Repair

George H.

George H.

ASE MasterTechnician

226 satisfied customers

15+ Years ASE Master Technician with Level 1 Certification

Don - Mo Lurch

Don - Mo Lurch

ASE Certified Technician

218 satisfied customers

GM, GMC, Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics

< Previous | Next >

Related GMC Questions
Idle engine. 285000 VVM envoy 2003 XL. Also battery not
This just happened todayhvnt had a chance to do anything as yet… read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
576 satisfied customers
The rpm and speedometer are inop on my 1996 Sierra truck. I
the rpm and speedometer are inop on my 1996 Sierra truck … read more
Gary
Gary
ASE Certified Technician
Vocational, Technical or Trade Scho
1,552 satisfied customers
Battery saver light came on. Battery test with the engine
Battery saver light came on. Battery test with the engine off at 12.7 VDC, With the engine running at an idle 15.7 VDC. Trying to locate the issue … read more
Mechanic01
Mechanic01
1,278 satisfied customers
No crank no lights in the speedometer and I chech with a
no crank no lights in the speedometer and I chech with a tester I found 8.4 volts in the radiator support help … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
576 satisfied customers
1997 GMC Suburban. Crank, but no start. Battery replaced.
1997 GMC Suburban. Crank, but no start. Battery replaced. Distributor cap replaced. Good spark, but no fuel on spark plug. Dropped gas tank and no power to fuel pump. No voltage across pins 87 and 30 … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Will not idle, just noticed that the negative battery cable
Will not idle, just noticed that the negative battery cable is disconnected, also there is a hollow line along the drivers side just under the hood that is broken. Not sure if this is causing the stal… read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,067 satisfied customers
Battery is dead all of a sudden. symble on dash = Battery
battery is dead all of a sudden. symble on dash = Battery malfunction It's a 2013 Acadia … read more
AZTechBrian
AZTechBrian
ASE Certified Technician & Shop Owner
Vocational, Technical or Trade School
732 satisfied customers
Will defective O2 detectors drain the batteries? New
Yes, Pulled fuses 1 by 1. Sitting idle battery is drawing 4 amps. … read more
roy
roy
Associate Degree
3 satisfied customers
I was cleaning the battery cables and reattached them and
I was cleaning the battery cables and reattached them and now the truck will not start. … read more
Jaybird61
Jaybird61
Master Automotive Mechanic
2,043 satisfied customers
I charged battery on 1999 GMC Z71, now my speedometer is
I charged battery on 1999 GMC Z71 , now my speedometer is stuck [ pegged ] at 100 mph . won't move no matter how much i pray and cuss . Help . … read more
heavy_chevy_396
heavy_chevy_396
Vocational, Technical or Trade Scho
2,518 satisfied customers
Battery light was on this am but alt is charging. Battery
Battery light was on this am but alt is charging. Battery was dead but is 6 years old. … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
I have a 99 GMC Suburban 5.7 speedometer not working. I have
I have a 99 GMC Suburban 5.7 speedometer not working. I have had the cluster rebuilt and all new vss's. I have ohm'd out the vss and have 1.4 k (ohm). I have checked the voltage and have 5 volts (AC).… read more
Gary
Gary
ASE Certified Technician
Vocational, Technical or Trade Scho
1,552 satisfied customers
2003 GMC Sierra pick up. Speedometer locked at 70 mph and
2003 GMC Sierra pick up. Speedometer locked at 70 mph and gauge for park/reverse/drive lights not on at all. All other dashboard lights comes on and drives fine. … read more
Jerry Newton
Jerry Newton
Vocational, Technical or Trade Scho
2,066 satisfied customers
I have a 1998 GMC Savana. The speedometer and odometer quit
I have a 1998 GMC Savana. The speedometer and odometer quit working. The odometer still lights up but doesn't change. No other warning lights are on and the cruise control still works.… read more
Dan
Dan
Automotive Technician
Vocational, Technical or Trade Scho
25 satisfied customers
Battery goes dead overnight, BAttery is good. Alternator is
BAttery is good. Alternator is good. I have pulled every fuse and can't find a circuit that is causing the draw. … read more
Gary
Gary
ASE Certified Technician
Vocational, Technical or Trade Scho
1,552 satisfied customers
Installed a new alternator and I did not unhook the battery.
Installed a new alternator and I did not unhook the battery. The starter wire touched something and sparked. Now my truck will not start, the lights will not come on interior or exterior, the auto loc… read more
AMEDEE
AMEDEE
AUTOMOTIVE TECHNICIAN
Vocational, Technical or Trade Scho
9,105 satisfied customers
GMC 2007 Roadtrek 6.0L 145 amp alternator. Battery warning
GMC 2007 Roadtrek 6.0L 145 amp alternator. Battery warning light on, volt output 11.7 volts; intermittent problem; equipped with dual battery isolator, sometimes it self corrects and voltage goes to 1… read more
eauto
eauto
self employed
High School or GED
74 satisfied customers
No crank no start everything comes on battery alternator
No crank no start everything comes on battery alternator starter is fine acts like it's the anti theft … read more
Chad Farhat
Chad Farhat
Owner
Associate Degree
4,096 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x