Alternator Failure, Voltage Spike!

Guys, had an all-off-a-sudden episode tonight on my way home. Car started fine, drove ok for 5-10 mins, then the air bag lamp started to flash (first time ever), then the climate control started to beep and change states by itself. Then the TC/ABS lamp came on, all of this within a minute. Finally I lost 4th gear and the trans started behaving erratically.

Scanned and found a code for voltage, scanner says 16.7 volts. Turn off car and battery voltage is 12.5v. What do you guys think?

The only thing i can think of that would cause that is a Voltage Regulator taking a shit inside your alternator.
How long since the Alt was rebuilt.?
Also, double check the resistance of the diode you installed. That could possibly cause a spike as well.

Yeah I was thinking the same thing. I had a similar problem in my 2000 Bonneville. I was getting these spikes on the dash guage, and sure enough thats what it was. Instead of having it replaced I just spent the $100 and got the reman alternator with the boosted output for the sound system

The alternator is old, installed in '03, 170k miles ago - that was my thought as well. But you've got me thinking about the voltage booster diode. If the sensor input was disconnected, it would cause the voltage to increase. I'll inspect the thermistor wire at the alternator and at the battery.

My first guess is bad voltage regulator. It could be caused or compounded by the voltage booster, but I've never heard of it before.

I just pulled up my rear seat. If you remember last year I pulled my OEM battery and taped the top back on. I think it's leaked some. So first thing I'm going to do is put in the Optima and inspect the area under the seat for damage.

Ok, the old battery was leaking (broken vent tube), so i took it out. Used baking soda solution to neutralize, installed the Optima. I don't think the battery was the problem.

Turned on the car, getting 17.2 volts on, 12.45 from battery.

Jesus......17.2V will fry all kinds of stuff. I agree with everyone and say Alternator. The diode has nothing to do with it.....it can't allow that much voltage through, even if it goes bad.

I tested the blue thermistor wire at 12.0 volts, so the diode and the wire are still connected and working correctly. Alternator replacement first thing in the morning. If all goes well, I'll be able to leave for work by 9:00a. Thx for the help!

New alternator at NAPA: $175 (+$60 core) - 7:30am
Begin install: 8:10am, finished: 8:40am

This had to be the fastest and easiest alternator swap in history. Now turning the key and crossing my fingers as I start the 30 min trek to work.

New NAPA alternator does not work. It was the last one they had. Guess it's off to the dealership.

Could you be more specific? Did it not fix the voltage spike or is it not working at all?

No output from the new NAPA unit. Car seems to run fine off battery, but it won't last for long.

Dealership wants $384 (!)

NAPA has not more in stock, Advance has none in stock. Autozone has two in stock for $149. I'm going to have them test the NAPA unit when I get there.

sorry to hear aaron, im not sure how long you can wait but a delco unit from rock auto is only $155 after the core.

while you are at it check the wire to the alternator with a voltmeter and wiggle it, see if it is maybe busted inside the insulation or at a connector. Should not be the case but it could happen. Kind of like the firewall wiring harness breaks on some Rivs. .

Albertj

This happens more frequently than these companies would like to admit. In the past I ordered a powermaster 100 amp alt and went thru three before I got a properly working one. One had a noisy bearing and the other was putting out over 17 volts. I find it odd that the factory unit can last 20 years or more but a replacement usually wears out much quicker. Apparently we haven't perfected alternator rebuilding yet.

That's the problem.....it's rebuilt cheaply by someone who is probably here illegally. If you're going to buy rebuilt, get the one with the lifetime warranty, otherwise buy new......

Quote :

while you are at it check the wire to the alternator with a voltmeter and wiggle it, see if it is maybe busted inside the insulation or at a connector. Should not be the case but it could happen. Kind of like the firewall wiring harness breaks on some Rivs.

I tried everything to get something out of the NAPA alternator. Since I had the new Optima in, I drove 7 miles on battery power to Autozone to buy a replacement. Before swapping, I had them test the NAPA unit on the car - failed diode check, no output except the battery voltage, which was down to 11 volts at that point. I had them print out a diagnostic sheet to show NAPA when I take it back.

After I installed the new alternator in the Autozone parking lot, drove another 25 miles to work, no problems. Car runs like before. I was worried the transmission would act up after what happened last night, but everything seems back to normal now.

PS - Drive with the rear seat out and it gets really loud in there!!! Incredible how much noise resonates through the sheet metal back there.

Man that sucks Aaron, all those systems going off at once would freak me out. It seems finding the right part for our cars in a pinch always proves diifclut (my battery experience). I hope it is the alternator, as others are suggesting and that it fixes everything once installed.

Yes, it sucks, but yesterday was just that kind of day. Key take aways:

- the car did not leave me stranded at any time
- the repair only cost $150 in the end (dealer wanted $400 just for the part)
- I was able to fix in only 1/2 hour (even though I had to do it twice)
- the OEM alternator lasted a solid 170k miles before failure
- no apparent damage to the car afterward, all systems are go

Compare this to driving a "more reliable" new car and paying $200-400 per month for that privilege; I'll just keep on driving my Riviera, thanks.

AA wrote:

Compare this to driving a "more reliable" new car and paying $200-400 per month for that privilege; I'll just keep on driving my Riviera, thanks.

Well said

Aaron,
Just out of curiosity, how much was the NAPA alternator.?
And was it a 150 amp instead of a 140 amp./

I had done some alternator research a while back and I remember my local NAPA had a reman for $190.00 yet it was rated at 150amps as opposed to stock at 140 amps.

It was a reman 150 amp - they do not carry a 140 amp. In theory the 150 amp is fine, as you can never have too many amperes, the system draws only as much as it needs. It's actually better to rebuild the alternator for higher current demands, should make it last longer. Having too few amps... that would be a problem.

You're right about the $190 option. Mine was $175. The guy at the counter told me the $175 option is a core with only the problem areas rebuilt + new bearing. The $190 option gets you a core with all internals rebuilt & fresh bearing, of course. They did not have the full rebuild in stock, or I would have bought it.

Last week I was getting a low idle sometimes and it would pop a code saying low voltage to sensors etc. I replaced the alternator, however, I forgot to disconnect the battery and the lead wire fell on to the engine giving off quite a spark! I disconnected the battery and finished hooking everything up. Here's what I got! The transmission feels like I have the brakes on trying to go forward, almost like it's blown. The Air Bag light blinks a few times and then stays on. I took it to a shop where they told me there were NO fusable links blown and they suggested getting a new computer. I did and had it flashed to the car. No change and its still running terrible. Barely Idles and tranny still feels blown. Checked every fuse everywhere and none blown. HELP PLEASE!javascript:emoticonp('')

First check all connections. Your low voltage to sensors codes should be a clue. This does not mean you had low voltage, or an alternator issue.

Disconnect the battery for an hour so the computer can reset. Then start it up and see what codes are thrown.

You quite possibly have a bad ground or loose connection. Sometimes underhood wires can become brittle and break at the firewall connector.