Possible electrical issue.

[smeppy]

Hi all. I was driving home from work tonight, about half way home the radio developed a barely audible hum, the cars warning chime went off one time and the red brake light (not the yellow abs light) and CEL lit up for 1 to 2 seconds, then everything went back to normal. The rest of the drive was uneventful.

There was no power loss that I could tell. No jerking or stuttering, nothing. Other than the momentary chime and lights the car was running fine. From reading some other threads, I will be stopping to get any potential stored codes read sometime tomorrow afternoon, and will have both the battery and alternator tested at Autozone. For what its worth the battery was replaced about a year ago. I will also check the battery and alternator connections for corrosion as well as checking the brake fluid level.

My serpentine belt has been squealing the past couple weeks. So I will have to check the tensioner to see if its going bad. I will check the brake fluid as well. The car has 124000 on the odometer and is a 2005 flex fuel vulcan, if that matters. Am I missing anything or is there something else I should be checking.

I don't have too much time to actually work on the vehicle, other than the simple stuff, courtesy of working 12 hour shifts. So any help is appreciated to avoid getting the run around from some of the fine mechanics we have up here in Pennsylvania. Thanks

[behlinla]

Sounds like you know where to start, so post back when you get some results.

[Jeff K]

Since you have an 05 with the message center, you can use Engineering test mode (ETM) to monitor battery voltage as you drive. Press & hold RESET with key off. Turn key on while holding RESET. In a few seconds "engineering test mode" will appear in the display. Release the RESET button and start the car. Pressing RESET will bring up a new display each time it is pressed. Several presses of the RESET button will bring up system voltage. You can watch system volts as you drive. It should stay relatively constant around 14.2 V.

[soundu]

Take 5 minutes out of your busy day, take the battery cables off
the battery and clean them along with the battery terminals as needed.
check the water in the battery while your at it. You would be surprised
how many people NEVER check the water level in the battery

[smeppy]

So I checked and reseated the battery connections. They were corrosion free and tight for what its worth. Stopped at Autozone and had the codes read, there was a pending ABS code for battery voltage out of range, code b1676 I believe. It struck me as odd since the yellow abs light didn't flash. While I was there I had them check the battery which came out normal at 12 volts.

They also checked the alternator, which did fail the diode test twice. I did use the engineering test mode on the way home from work and of course the car didn't act up. The voltage bounced between 14.2 and 14.7 while the car was under load, and dropped to a low of 13.5 while sitting at a red light.

I will keep using the etm to monitor voltage as I am driving the vehicle just to see how bad the voltage does get when this happens again. The serpentine belt squeal as far as I can tell is the tensioner. Though I don't have a mechanics stethoscope to be precise. That pulley however was feeling a little rough when I spun it, not horrible but it didn't spin as freely as the others. Given the mileage I'm guessing its probably a good idea to replace the idle pulley and belt as well.

Unfortunately I wont be able to replace the alternator until payday, a week from today. Yay for going Christmas shopping for the kids last week before the light show on the dash. The only other question's I have are could this just be a result of the tensioner ? My uneducated guess is that since the alternator failed the diode test it needs to go regardless.

Does anyone have any recommendations for alternators ? Is it a good idea to buy it from a local store just so I can have them bench test it before I buy it. I really don't want to replace a failing unit with a potentially bad unit.

Regardless I will have it sorted by next Thursday unless someone more knowledgeable chimes in otherwise. If all else fails I can use the wife's car to get back and forth.

[behlinla]

Originally Posted by smeppy

They also checked the alternator, which did fail the diode test twice. I did use the engineering test mode on the way home from work and of course the car didn't act up. The voltage bounced between 14.2 and 14.7 while the car was under load, and dropped to a low of 13.5 while sitting at a red light.

Well, that answers that. Diodes do not fix themselves, so you'll have to get a new alternator. Voltage should not move around that much either (should stay ±0.2 volts).

Poor belt tension can cause alternator problems, but usually it's sporadic and related to the current electrical load. For example, if you turn on the rear defrost and headlights and the voltage goes crazy while you hear squealing. But again bad diodes aren't caused by belt tension, so the alternator is bad.

I agree you shouldn't buy an alternator unless it's been bench tested. I would try to avoid the Autozone house brands.

[soundu]

Originally Posted by smeppy

So I checked and reseated the battery connections. They were corrosion free and tight for what its worth. Stopped at Autozone and had the codes read, there was a pending ABS code for battery voltage out of range, code b1676 I believe. It struck me as odd since the yellow abs light didn't flash. While I was there I had them check the battery which came out normal at 12 volts.

They also checked the alternator, which did fail the diode test twice. I did use the engineering test mode on the way home from work and of course the car didn't act up. The voltage bounced between 14.2 and 14.7 while the car was under load, and dropped to a low of 13.5 while sitting at a red light.

I will keep using the etm to monitor voltage as I am driving the vehicle just to see how bad the voltage does get when this happens again. The serpentine belt squeal as far as I can tell is the tensioner. Though I don't have a mechanics stethoscope to be precise. That pulley however was feeling a little rough when I spun it, not horrible but it didn't spin as freely as the others. Given the mileage I'm guessing its probably a good idea to replace the idle pulley and belt as well.

Unfortunately I wont be able to replace the alternator until payday, a week from today. Yay for going Christmas shopping for the kids last week before the light show on the dash. The only other question's I have are could this just be a result of the tensioner ? My uneducated guess is that since the alternator failed the diode test it needs to go regardless.

Does anyone have any recommendations for alternators ? Is it a good idea to buy it from a local store just so I can have them bench test it before I buy it. I really don't want to replace a failing unit with a potentially bad unit.

Regardless I will have it sorted by next Thursday unless someone more knowledgeable chimes in otherwise. If all else fails I can use the wife's car to get back and forth.

I would be interested to know what they meant by diode failure. They
usually fail shorted. When that happens, there is a constant drain
on the battery, the alternator will be warm long after the car is off,
and it will run the battery down just sitting.

The alternator is a three phase electrical generator. My guess is one
of more of the diodes has failed open, causing the alternator not
to put out its rated current output and have a abnormal output waveform.
Now, if the solder came off where the diodes are soldered in, there is a
chance to repair it internally. But you would have to tear the alternator
apart, and have a BIG ASS soldering system to have enough heat to
do it.

If your on the cheap, you could always go to the UPuLL yard and look for
one. On my trip to the local yard this week, i saw at least three on
GEN3's that had rebuild stickers on them and looked relatively fresh for
about $30.

Dont screw with the tensioner or idler wheels too long. I had one once
on my 93 that self destructed and shot the mount bolt out into the
windshield washer tank in a act of self destruction. If they are not spinning
freely, replace them. It going to be cheaper than a tow. as long as your
there, get a knife or blade or such and clean out the groves in all the
pulleys. Also look for leaks that can be putting oil or water on the belt
causing it to slip under load.

Your voltage will vary at lower RPM's depending on the load. If your running
headlights, heater blower, and other stuff your NOT going to get full output
at idle.