2008 Envoy - Intermittant RAPID Battery Drain w/ key off

Asked by ChuckLS7 Feb 03, 2020 at 12:47 PM about the GMC Envoy

Question type: Maintenance & Repair

2008 GMC Envoy . . Rapid Battery Drain (12.5 down to 5.0 in 2 hours) . . Related symptoms or oddities - NONE (no lights on, no noises or sounds, nothing). . Frequency of problem occurring - 3 times during the past 20 days . . Voltage after 2 hours - around 5.0volts, and dropping (I say 2 hours, because that just happens to be how long it was, from the time the ignition was turned off, to the time that I was able to check batt voltage with a meter . . 1st time it happened (wife driving, I'm not there) - parked the car - came back to it an hour later - had inter lights - had dash lights and open door chimes, but no starter - She called - I asked her to turn on the haedlights and beep the horn - both worked - I got to the car 45 minutes later - tested voltage at the batt - (by now, 1 hr and 45 min after parked) it was down to  5.2volts, and still dropping - hooked up cables - let other car run, to "charge" the Envoy batt for about 5 minutes - then, Envoy started fine - dashboard volt meter (and hand-held meter) near 15v - lights normal - drove home normal - did a batt and alt test, both good / normal - (?) - maybe a UFO flying low (?) - everything working fine / normal for the next 10 days or so . . 2nd time it happened - same, turned car off - went to use it a couple of hours later - dim inter lights - had dash lights and open door chimes, but no starter . . We were due to be somewhere, so took my car . . got back to the car a couple hours later . . Tried to start again (just for grins and laughs), and got a brief reaction from the starter, but not enough to actually start - this tells me that whatever wad drained the batt, before we got in and tried to start the car a couple of hours earlier, had "jogged" during that initial attempt, and so, the batt stopped being drained, and had, by then, stabilized enough juice back at the positive terminal, to actually have more voltage there, than when we tried to start it before (when it was still draining, and the voltage was really low at the pos term) . . Did a voltage check - 11.something . . Knowing (figuring) that the problem didn't exist (wasn't showing / wasn't traceable) at that moment, I did another jump / charge / start / alt test - all normal . . After that 2nd occurrence, (and wanting to figure it out) I started driving the Envoy myself (driving the wife to work and back every day) hoping to "catch it in the act", and be there when it happened (and while it was still draining) so I can finally do some tests, during the only time that might actually show me something . . So, I'm checking voltage, several times a day (and night), for the next week, and I'm getting normal voltage, normal starting and driving, until…. The 3rd time it happens, at home, in the driveway . . Yes! . . I can finally MAYBE find something, before it "corrects" itself, and stops draining . . I'm careful NOT to turn the key on, or even have it in the ign., no opening or closing doors, etc, so that nothing can jog the problem back to acting normal . . For that entire week leading up to this 3rd occurrence, I had left both driver's side doors open (letting the inter lights cycle off), for that same reason . . I had realized THIS (the 3rd) voltage drop occurrence, by chance, during one of my numerous walk-by voltage checks, and it was already down to 5.0 volts (not certain how long it had been, since the previous check, but it couldn't have been more than 2 or 3 hours) . . So, with my hand-held meter on the batt, I started pulling fuses from the front fuse box, and watching the meter after each fuse pull, reinstalling each fuse, still watch the meter, before moving on to the next fuse . . then circuit breakers, then relays . . No "abnormal" changes in the voltage readings, and the batt voltage continued to drop . . Moved to the rear fuse box, meter now attached there . . Same deal there - no abnormal changes, EXCEPT for the RADIO fuse (#27) . . When that fuse was removed, voltage stopped dropping, and then, the voltage crept up (over the next 5 minutes or so), stabilizing at about 8.0 volts . . I made sure that nothing was touched or moved, during that 5 minutes . . The radio fuse just happened to be the last fuse to pull, in that rear box . . Once the voltage had stabilized around 8.0 volts, I re-installed the radio fuse, just to satisfy myself that I had actually found something, and the voltage instantly dropped to about 6.0, and continued to creep down, until I pull it back out . . Did this another time or 2, nodding my head and grinning . . With that fuse out, I continued with that box, pulling circuit breakers and relays, finding nothing there to consider . . I had already (days before) pulled the On-Star fuse (#43), as it isn't being used, and since I had read that this system can malfunction, causing continuous attempts by the system to communicate with OnStar's satellites . . Shouldn't be enough amperage to cause the draining that I'm having, but why not eliminate it, just to remove it from the list of possibilities, right? . . So, before leaving the rear fuse box, just for grins and laughs, I plugged the OnStar fuse back in (radio fuse still out), and it produce pretty much the same result as the radio fuse . . initial 1.5 volt drop, followed by voltage creeping down further, until removed again, when voltage then goes back up . . Done with the rear box, I moved back to under the hood . . With my meter attached to the batt, I unbolted the terminal going from the batt to the front fuse box, disconnecting both boxes, and saw an acceptable / normal voltage increase of maybe 0.02 (don't remember exactly, but not enough to consider) . . With both boxes disconnected, I then tested for draw from the only 2 things left, the starter and alternator . . Voltmeter across the batt terminals, with both batt cables still attached to batt, then with the batt + red cable disconnected . . Zero voltage change . . I re-connected the batt-to-fuse box cable, partially waking up a thing or 2 (the interior lights came on, dim, and drew the voltage down a volt or 2,but didn't seem to stay on but a few short seconds - not the usual amount of time) . . I went back to the rear box, and re-installed the radio fuse, but it now had very little effect, in or out (so, I'm guessing that re-connecting the fuse boxes somehow "jogged" things back to "normal", and the severe drain went away, once again . . I'm probably going toned to hear from someone who has experienced this exact same problem, and not just the typical parasitic current draw, that will cause a "batt just too low to start", after a couple of days or so . . This particular Envoy's issue is dealing with a good 12.5 battery being taken down to 5.0 (and still dropping) in 2 HOURS or less . . If the draining stops, while the batt is at, let's say 5.0 (5.0 while it's still draining), the voltage will pretty quickly rise to about 7.0, and within 4 or 5 minutes, will stabilize at about 8.0 or even 9.0 . . So, that's about it, guys . . The only other thing, that might be worth mentioning is, I've noticed that the dash volt meter (check against my hand-held, several times) shows pretty "normal range under normal conditions" readings, but after driving for 10 or 15 minutes, rather than stabilize at 14.0 (+/- .1 or so), the final stabilized number is about 13.0 (handheld shows 12.89 - 13.02) . . It will stay right there, at idle or driving, indefinitely, until the key is turned off, and the engine is re-started, which starts a new cycle (first, high 14's . . after 5 minutes or so, 14-ish . . after 10 minutes or so, 13-ish) . . So, can that staying at 13-ish be related to the intermittent rapid draining when the key is off ? . . Aside from the draining, and the 13-ish thing, everything else about the Envoy's functions and performance seems very normal . . So, if anyone out there has experienced either (or both) of these issues, PLEASE pass along your experience (and a cure) to me, as I'm just wanting to get to the bottom of it, and make the wife happy . . Sincerely, . . A lover of much older cars, . . Chuck.

1 Answer

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You did a parasitic draw test, and narrowed it down. Don't believe you'll get a cure here in this forum for something this technical. Go to gmtnation.com copy and paste this. It's a site for our Trailblazer/Envoy platform. They'll get you hooked up, I know for a fact there is an electrical engineer there that owns an Envoy himself.

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