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post #1 of 40 (permalink) Old 04-06-2017, 10:18 PM Thread Starter
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Alternator light on, need advice

My alternator light came on yesterday along with the battery light so I didn't drive my G8 to work today because of it. I got my multimeter out and checked the battery voltage and seems normal(12.6v) then tested it again with the car on(14.7v), then with accessories running(14.2v). From recent reading those all seem fairly normal. I decided to take it to orileys to have them do a quick test and they guy tested to battery and said it passed. Started it up to test the alternator and he said that reads fine as well. One thing he suggested was to put on a new belt, I'm at 86k and still original belt. I haven't inspected it in a while and probably need to. It's been rainy here and his thought is the belt could be wet and slipping causing the alternator trip from insufficient power. When I left I started up with engineering mode and voltage was reading 14.7 but did go up to 15v til I got home. Only like a 5 minute drive.

The light is still on and since the light came on yesterday I probably have had a total of 15 minutes drive time. I could change the belt but don't want to get stranded if it more than that. Not sure if the light coming on means do not drive the car at all or if I have some wiggle room to drive a bit to test if a new belt could fix it. I could drive in engineering mode and keep and eye on the voltage but again don't know if that's a bad move as well. Can I trust the test they did with their tool that my battery and alternator are fine?
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post #2 of 40 (permalink) Old 04-07-2017, 02:28 AM
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Utilizing the handheld starting and charging system tools commonly found at Napa, O'Reilly, and AutoZone are reminiscent of having the check engine light come on, scanning the vehicle for codes and obtaining a printout of fifty to one hundred things it could be. At best, they'll put you in the ballpark or near vicinity of the problem. At worst, you'll be chasing unconfirmed sightings of Big Foot wasting both time and money. Had both an alternator and battery fail on separate vehicles shortly after being told everything checked out fine by the counter "technician". They are merely good resources to help isolate and pinpoint the problem, but shouldn't be solely relied upon. On a different note, was told that bench testing a starter, battery or alternator is more accurate than testing one on a vehicle, but either the person didn't know or couldn't explain why. Believe their handheld systems mainly check current flow i.e if the alternator is producing the right voltage, so forth and so on. Try checking the plug-in connector on the back of the alternator for frayed, damaged, or loose wiring. Check the stud bolt (alternator ground) as well for a good connection by making sure the nut is properly seated against the wire. Prior to starting the car, check the tightness of the belt by pulling upwards as it should have plenty of resistance. Visually check the rotation and movement of the alternator pulley while the vehicle is running. Does it spin freely? Visually check for belt looseness as it travels along the various pulleys for bulges or inconsistencies. The serpentine belt is designed to last well beyond 100,000 and yours should much of its useful life remaining. The charging system light indicates it is not being charging properly and the alternator message on the driver information center indicates it is not providing ample power to charge the system. The battery supplies power to the starter motor and turns the pinion gear which in turn engages the flywheel and starts the engine. If you must drive the G8, remember to turn off an unnecessary accessories such as the air conditioner and radio to reduce the power draw and prolong the longevity of the discharging battery. The charge on the battery is going to determine how long and far you will be able to drive the car in its current state. Probably way much more than you were asking, but hopefully this helps. Best of luck

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Last edited by PONY MAN; 04-08-2017 at 01:32 AM.
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post #3 of 40 (permalink) Old 04-07-2017, 08:07 AM
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Don't trust a hand held battery checker.

My battery failed in the wave of 3 yr battery failures on the G8s. Dragged the battery with me to Wmart just for the core charge. They checked it with a hand held device and said it was still good and I don't need a new battery. I said keep the battery.

(The $120 replacement battery is still working fine)
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post #4 of 40 (permalink) Old 04-07-2017, 09:27 AM
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Honestly, a Multimeter and the knowledge of what you're looking at is all you need. You can't just do a voltage check and call it a day. Voltage can be right on the money, but you need check resistance, too. It doesn't hurt to check for continuity through ground.

Of course, if it has a short to ground, it fries itself. Electricity takes the path of least resistance. That's why a dryer that overloads doesn't fry the person who's touching it... The copper ground line offers little resistance compared to your finger. So you'd get a sudden current spike and that'd be it for the alternator... So if THAT has happened, you're on borrowed time (my favorite expression of the week ).

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post #5 of 40 (permalink) Old 04-07-2017, 11:02 AM Thread Starter
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Thanks for the replies. PONY MAN your post was great and informative. I will check out the stuff you said after I get home today. I quickly felt the belt this morning, felt tight and looked like it's in good condition. I am at 86K miles tough. Still as you said I also found posts stating these belts can last a while. It was a bit dark in the garage so I'll check it again with more light today. I didn't think I could fully trust that test and feel like I'm on borrowed time. Just want to figure it out by middle of next week my wife will need her truck back.

My battery was a new install in 2012 when I bought the car. I know this because after I bought it and started to use the trunk, I noticed everything had a damp feeling. Threw some baking soda on it and fizzed. Checked is all out and a pool of acid was in the spare tire well. The dealer had to replace everything in the trunk, carpet, spare tire well, repaint and install a new battery. So the battery is coming up on being 7 years old.

Engineering mode says the life is at about 64.1%. Wondering if that is too low, my old cars never have this kind of info in them so not sure how reliable this really is. I did find a youtube video by a guy named ChrisFix showing how to test a battery and alternator. Seems good but I'm not too knowledgeable with electronics but he seems to go over how to test these with a meter.

Thanks for the info so far guys and I will check out the point from your posts. If I come up with nothing from this maybe I'll start with a battery then move to the alternator I guess. I'm hoping I get pointed to one or the other so I don't have to start guessing and replacing.
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post #6 of 40 (permalink) Old 04-07-2017, 11:11 AM
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In thinking further, since it's outputting voltage, resistance is the key test here............ Shorting to ground should result in a voltage drop.

'09 PSM G8 GT - Current Mods: Solo Axle-Back w/ X-Pipe OPG CAI. SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
Mods Planned: DOD-Delete, Stage 1C Livernois, Kooks Mids, GXP Trans Cooler, 2800 Circle-D Stall Converter, Differential (Max 3.45)

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post #7 of 40 (permalink) Old 04-07-2017, 04:46 PM Thread Starter
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So I checked some of this out and when I pulled the positive cable off the car died instantly. Seems from what PONY MAN said alternator must be bad. I put the positive back on have have more bad news, the dic is no longer working. Any ideas? Did I just fry something by doing that?
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post #8 of 40 (permalink) Old 04-07-2017, 06:01 PM Thread Starter
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Checked the fuse for the IP and is fine. Just in case I swapped one of the others and still nothing. Whole IP is out, display gauges and lights.
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post #9 of 40 (permalink) Old 04-07-2017, 06:39 PM
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The G8 charging system is "new school" - many folks will give old school advice that may not apply while trying to help. Here is a document that details the charging system - should give a good backup to know where to dig.

charging system

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post #10 of 40 (permalink) Old 04-07-2017, 08:18 PM Thread Starter
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Unfortunately I think the old school approach may have fried my cluster. Going to be an expensive mistake I'm guessing and probably going to have to do something I avoid at any cost. Go to the dealer to get it checked and just have them check the alternator/battery while its there. The dead cluster I now have is something I have no idea what to do with other than checking the fuse. Lesson learned from that.
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post #11 of 40 (permalink) Old 04-07-2017, 08:30 PM
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Shoot.... I thought you'd just check a few leads on the alternator......

Years ago, the positive cable being disconnected didn't have a bunch of electronics that it could damage. It STILL could damage a battery if you were to accidentally touch metal to the chassis... Today, there are a lot of electronics in the way... Of course, fuses protect today's electronics. So you may be alright..

'09 PSM G8 GT - Current Mods: Solo Axle-Back w/ X-Pipe OPG CAI. SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
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post #12 of 40 (permalink) Old 04-07-2017, 08:49 PM Thread Starter
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Yeah I did put a meter on it and was still testing fine so went ahead with the disconnect advice without checking to see how safe it was to do. Feel pretty dumb about it because a few minutes on google would have told me that's not at all a good idea to do. I checked the fuse box above the battery for the IP, looked good, swapped with another fuse to be sure and still nothing. My 1 problem turned into 2 problems from that bad decision.
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post #13 of 40 (permalink) Old 04-08-2017, 01:04 AM
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Edited previous post due to it being very inaccurate and incorrect information. Perhaps it applied to earlier vehicles, but after researching the "old wives tale", it is far from the truth. No, you aren't the dumb one, rather it's me for taking someone's word at face value without investigating the notion any further. Will go out in the morning and pull the fuse in the rear compartment fuse block (F5) for the instrument/display/remote function actuator/data link connection panel to see if the driver's information center stops working. Unsure if the driver's information center is powered by the body control module which operates on a separate fuse, but guess it wouldn't hurt to check each fuse individually.

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post #14 of 40 (permalink) Old 04-08-2017, 01:27 AM
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Just get an Alt. from Amazon for 195 bucks, swap it out and be done....

I just changed mine and the serp belt 2 months ago. Thought maybe my belt was slipping since it was oem, replaced it and nothing changed. Got my hands dirty and changed the alt out...no more problems.
Its about time for it to go bad man... just go with the simple.

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post #15 of 40 (permalink) Old 04-08-2017, 08:22 AM Thread Starter
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I checked the BCM fuse and swapped it with another. Still nothing. 5litrarag, that was the plan until I screwed up my IP. Going to have to take it in I guess.
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post #16 of 40 (permalink) Old 04-08-2017, 10:02 AM
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Turned the ignition on to verify operation of the instrument cluster. Removed the F5 (red-10amp) fuse for the instrument panel located below the F2 (green-30amp) for the amplifier and the display went dim. Read on a different thread were a member had the same problem (very different circumstances) and it was remedied by disconnecting the battery for an hour or so. Sending a pm shortly.

#AUDACITY OF HOPE

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"Nature never repeats herself and the possibilties of one human soul will never be found in another". -Elizabeth Cady Stanton






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post #17 of 40 (permalink) Old 04-08-2017, 10:57 AM Thread Starter
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PM'd you back PONY MAN.
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post #18 of 40 (permalink) Old 04-08-2017, 11:53 AM Thread Starter
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Took the IP out, how would I test to see if its getting power. PONY MAN suggested to check this but not really sure where to go from here. Any ideas?
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post #19 of 40 (permalink) Old 04-08-2017, 03:02 PM
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They show 15 wires going to that 18 pin IPC connector. Of those, 2 wires are for power to it, an 1 wire is a ground return going from it. All the rest are logic type wires wires (like at 6 from the steering wheel control switches), 1 for the MIL light, 1 for the car armed light, 1 for the brake light, 1 from the DLC, an (if installed) 2 wires from the inside mirror circuit. If you have your meter handy, check for B+ power at pin #1 (power at all times). It is OG/WH in color. Wire #10 (PK in color) is ignition switched power. An pin#9 (black in color) is your return ground. If you can verify that those 3 wires are doing their thing, but will not power up an test itself, I would have to lean towards a failing IP cluster.
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post #20 of 40 (permalink) Old 04-08-2017, 03:18 PM Thread Starter
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So pull the pins out of the harness? Sorry, electronics are not my strong suite, obviously. Just not sure how to get my meter on the wires to test.
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