On the '05 Nissan Quest I have a Scangauge hooked up to the OBDII connector. I have the gauge set to MPH, RPM, Volts and Water Temp. I have noticed this weekend that the Volts are often reading in the 10's and 11's but very rarely reading greater than 12. I think in the past that the gauge often reads 13s & 14s.
The battery is a Walmart unit of proper size with 585 cca and a tag saying it was manufactured in 11/15 or about 10 months ago. The battery was already in the car when I bought it in April. Since purchase I have added about 10k mostly trouble free miles.
Currently, the van is driving perfectly.
Does this low volt reading mean that I have a alternator going bad?
Battery voltage, when engine is off should be 12 volts or more. Try disconnecting the battery, while the engine is running. I suggest insulated gloves or tools while doing this. If the engine stops, it's the alternator.
At very least I would get it tested.
I would also load test the battery after putting it on a charger for a couple hours.
In modern cars I am not a fan of taking the battery out of the electrical system. The modern computers ate much more susceptible to voltage spikes and drops. The battery acts as a buffer or electrical shock absorber if you want to think of it that way.
T.J.
UltimaDork
9/6/16 9:40 a.m.
In reply to dean1484:
Yes - I agree. I would never intentionally disconnect the battery on a running car, especially a modern one as a way to test the alternator.
Check voltage at the battery while running with a voltmeter and verify your numbers.
T.J.
UltimaDork
9/6/16 9:42 a.m.
That is a low voltage. Did you measure the voltage directly at the battery terminals with a voltmeter both with the engine off and running?
I just went out and turned the key forward but did not turn so far as to start the car. Volt gauge reads 10.0 
I put on the charger and it reads low also. I'll keep it on the charge for the rest of today and continue to monitor while prepping for an alt.
Load test the battery as well.
The low voltage means the charging system isn't working, but it doesn't necessarily mean the alternator is at fault. It could be the voltage regulator, there could be a loose or broken wire somewhere, or the battery may be dying.
kb58
Dork
9/6/16 10:22 a.m.
gearheadmb wrote:
Check voltage at the battery while running with a voltmeter and verify your numbers.
^This.
Charging the battery isn't going to fix anything and it'll just happen again in a few hours. Yes, the alternator or regulator... isn't. Remove the alternator and have it tested at any parts store.
Most modern cats won't run with the battery disconnected. That was a great test in the 60s, but not a good idea anymore. As mentioned, you should have 12.xx volts with car off and 14.xx with it running at high idle. If not there are problems in the charging system, which covers the alternator and a bunch of other parts depending on the car.
Amazon can have this $142 (w/tax) Aftermarket, new not reman here on Thursday.
Rock Auto had a little cheaper even with shipping but no guarentee to get here even this week.
Box stores started at $175 and when up from there. None were in local stock but likely next day.
Any reason I shouldn't?
True, not sure if I need an alt but I need to keep the car on the road and I can return the Amazon if I do not need.
Confirmed via all the parts stores...there seems to be no separate voltage regulator (internal.)
Arrg mine does this too.... Not as bad yet, I guess I should order an alt or brushes too
https://www.youtube.com/embed/LDd4Rn4lpFU
Local Oreily's had this nice Auto Meter Brand electrical tester with a msrp of $899 as a free service!
It came back with the answer of battery good, volt regulator bad.
My O'reily's store has really nice equipment. When I had an ABS light on another car they were the only box store that had a free code reader that could read ABS too!
In reply to java230:
I think that looks pretty normal.
How many "book hours" is it to change the alt in a '05 Nissan Quest?
Time for me to research if I'm doing this myself or sending it out.
jstein77 wrote:
In reply to java230:
I think that looks pretty normal.
Sorry to jump on your thread John....
Really even dipping that low?
No jump. Welcome. Come on in.
Book time for 05 quest alt is 2.2hrs on Mitchell
Requires pulling the radiator for access.
In reply to Run_Away:
Glad to have your reply.
Not so glad to hear about the radiator.
T.J.
UltimaDork
9/6/16 9:45 p.m.
What is the conversion factor to go from book time to actual time for a guy in his driveway or garage who's never done this exact job on this vehicle before and instead of a factory service manual only has youtube and this forum for information?
That varies greatly on your skill level.
Quest alt is not a job that is really any easier with a hoist or power tools. Drain rad, pull fan assembly (real tight by the battery tray, you'll have to bend plastic a bit to squeeze it past), pull rad, remove RF wheel, splash shield, remove outer belt and tensioner, remove alt. Re-assemble, top coolant and ATF.
So little goes wrong with an alternator, it is cheaper to have a local electrical shop fix it.
They will check the rotor and stator. Failure rate is low for these. There are diodes, failure rare.
Biggest cause and a wear item, especially on high mileage units is worn out brushes that are not making contact with the slip rings.
Depending on the year, late model units have the voltage regulator in the ECU. One reason not to disconnect the battery.
I wouldn't trust a cheap new Chinese alternator (think of all the ways corners could be cut) more than I'd trust a parts store OEM alternator rebuilt in Mexico that has a warranty you can easily use. A local rebuild is the best if you aren't selling limbs for a new OEM unit.
