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Starting and electrical issues

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Gugmuck, Dec 7, 2012.

  1. Gugmuck

    Gugmuck New Member

    I have a 2008 Silverado 1500 5.3l Z71
    A little while ago I starting having issues starting; they were very intermittent, only happening once in a while but started becoming more and more common, resulting in multiple times a day.

    The key fob works to lock/unlock the truck, I have full power to everything when I turn the key to the on position. Radio works properly, lights come on, everything. When I attempts to start the engine, I hear a single click, the power dies and then comes on and the radio/clock/temp controls are all reset. Occasionally this reset also happens when the truck does start properly also.
    As per many suggestions from friends, family, etc. I cleaned battery posts, checked that cables were tight and gave the starter a good smack a couple of times. All to no avail. Occasionally, the remote start also cuts out. I get the same 'click' from the engine, then nothing.

    If I boost the battery, it fires up instantly and works for anywhere between a couple of days and a couple of hours before this happens again.

    I get an intermittent engine code.. comes and goes, and it is P0121. When the truck will not start, the battery generally sits around 8.5-9.5V.

    Also at random times, regardless of whether there are starting issues or not, the information display will inform me that Traction Control, Stabilitrak, Trailer Brake Controller and ABS all shut off and need to be serviced.

    I replaced the battery and these issues seem to have gone away so far.. however my lights dim slightly when I use things like electric windows, or sometimes when I accelerate.

    I have been told that my voltages are still a bit low (a self proclaimed mechanic friend at work) and I am worried that the problem has not really gone away, rather just postponed.

    I brought it to a shop and got it back within the hour with the response of they don't know what is wrong. (I get the feeling they didn't really try all that hard) Any help or suggestions would be greatly appreciated; I need to resolve this soon as I live in Canada and it is definitely not preferred to be stuck in the cold without heat or travel this time of year lol.

    Thanks :)
  2. sodbuster

    sodbuster New Member

    I would check a couple things, first after your truck sits for a while take a multimeter and check the voltage, should be north of 12v more like 12.5. Anything less than 12 and you have a bad battery, or charging system. I know it's new, but it could be defective. Second, I would take the multimeter and measure the voltage across your battery terminals with the engine running, mine runs at about 14.7 - 14.9. Maybe your alternator is on its way out. SB
  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Like the previous poster stated check the alternator.
    I suspect the original problem was a bad battery, dead cell, but it sounds like you also have a alternator thats on it's way out.
    Either check it yourself or have it checked on a test stand, I prefer a test stand since they can load it accurately and get a better picture of whats happening.
    Also check the grounds from battery to frame, starter, body, etc. some of these grounds may be developing corrosion aggravating the problem.
  4. Gugmuck

    Gugmuck New Member

    Alright, sorry it took a bit, but I haven't had the chance to come back online until now.

    While off, I get 12.2V
    While running I get an even 15V

    This was done myself, as I haven't had the chance to find myself a testing place.
    Also, yesterday half way home from work the Stabilitrak/ABS/Trailer brake problem came back. Disappeared after the next start.
  5. j cat

    j cat Rockstar 4 Years 1000 Posts

    with 15 volts at the battery with the engine on it must be 10 deg F or lower on first starting the vehicle to get that high a reading.
  6. jake's silverado

    jake's silverado Epic Member 5+ Years 100 Posts

    So awhile back I had a similar issue, battery ran down easier as the temps started to drop. Long story short I would need to boost it every morning or once in awhile I was lucky and didn't need to boost. What I did was hook up a meter to monitor the current draw, and the draw when the car was off (if my memory serves me) was about 30 mAmps, but after waiting about 10 minutes I could hear some relays and cracklin noises in the speakers and the current draw actually jumped to about 3 amps then slowly drop to 300 mAmps. Turned out to be a bad Body Control Module Not sure if this helps you but there's my experience with similar circumstances...but in my 2000 Impala.
  7. Gugmuck

    Gugmuck New Member

    As it is winter here, the reading was taken at around -15 Celcius (5 Fahrenheit) Though the problems started at a much higher temperature, during late summer. So I'm not sure what difference this makes..
  8. Pikey

    Pikey Moderator Staff Member 2 Years ROTM Winner 1000 Posts

    Do some research if you have your alternator tested. Some alternators will be damaged during an off the vehicle stand test at a place like Autozone. My 05 is regulated by the PCM and does not have an internal regulator. if you put it on a stand tester it will fry it. I learned this after having one fried at autozone. We walked over to the computer to look up a new alternator and the computer clearly stated "Warning: Test ON vehicle only, failure to do so will result in damage". When I bought my new alternator from Bosch the included paper work had the exact same warning. I looked into your vehicle, The autozone site carries the same warning for your truck. I recommend that if it tests bad and you have the Bosch style, that you do not buy a reman. (I had major issues with remanned bosch style alternators) You can get a new one directly from bosch cheaper than what autozone wants for the reman. If the alternator tests good, then I would start looking at ground wire problems.
  9. j cat

    j cat Rockstar 4 Years 1000 Posts

    the voltage regulator is throttled by the temp of the alternator. 15volts is the max end of the range. 13volts is the low end of the range.

    with the vehicle driven 20 miles and fully heated up with your cold temps the voltage should be around 14.25volts.

    what I have found is in cold areas with the us of road chemicals the internal circuits of the regulator do get damaged. the voltagecharge will drop out intermittently at first.

    with the dimming of lights with the operating of the window/seat etc. this is usually the diodes in the alternator. instead of a full wave rectification you have 1//2 wave. your total power is now 50% less , though the voltage output under light load will not show with lower voltages only under high loads would this be revealed.

    If it is determined you need an alternator do not get any rebuilt alternator. these are damaged. the alternators made for use in todays world run very hot, much hotter than a 1990's vehicle and older.

    in the old days a rebuilt was not a bad idea. back then these would last 200.ooomi then just clean up and replace the brushes. not today !
  10. Gugmuck

    Gugmuck New Member

    Alright; so I know it has been a long time since this thread was started, (have been out of the country with work) but when I got the time to look into it again, I came to a bunch of dead ends just as the first times. Upon arriving home this time around, I found that I now had an intermittent cruise control issue to add into the fray. Finally gave up hopes of fixing these issues myself and brought the truck into the shop. It turned out all issues could be attributed to the brake light switch. Upon applying the brakes, the switch would not recognise that I had released the brake pedal and would shut off the services in order to save them from damage or some such. I thank you all for your suggestions, the help was greatly appreciated! :D

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