Alternator Monitoring

[dbaxter_ss]

Is there a way to monitor if the Alternator is going out?
I have the battery volts, which at startup are around 11, driving around 13.1. Battery is less then 4 months old, but alternator is stock.

I have the ASP alt pulley on it now and swapping back to stock this weekend.

Just wanted to see if there was a way to confirm the alternator is just not performing as it should.

[Blacky]

In PID {GM.STATE00} is a flag called Alternator L terminal. Basically it just tells you if the alternator has failed, not if it is performing poorly.
I do not know of any other scan PID related to alternator performance.
Paul

[joecar]

Engine off, battery should be no less than 12.4V.
Starting, battery should be no less than 9.0V.
Running alternator will put at least 13V (or more) across battery.

If you see 11V with engine off, your battery has one or more dead cell(s).
If you see less then 13V with engine runing, alternator is dead;
if you see more than 17V with engine running, alternator is also dead (the integrated regulator is dead).

Alternator has output to PCM for "not regulating" (which ends up being displayed on dash as the alternator/charge idiot light).

[dbaxter_ss]

Thanks for the info:

I put the pid on Paul recommended and its always with a little red dot and NO VOLTAGE :(

Its normally running around 13.1 but at lights and idle between 11-12 :( :(

Bummer Sounds like the ole alternator has had a better day.

Battery should not be dead ( or better not be I just got it ) but I will go out and just click her on but not started to make sure.

[Steve Bryant]

Your alternator may be OK and you battery may be fine too. It may just be the underdrive pulley situation that's getting to you. 13.1 Volts in the summertime and around 13.8 Volts in the winter time until the engine warms up are fine. The alternator voltage regulators are temperature compensated to give you a higher voltage initially in the winter (until the alternator case and internals warm up) and lower voltage in the summer. This gives you a higher state of charge on the battery for winter starting and prevents water evaporation from the electrolyte in the summer.

The alternator shaft spins at maybe six times crankshaft RPM's with stock pulleys to give you good voltage and current even in the idle to 1,500 RPM range with high electrical loads (air conditioning and other power accessories) as are typical these days. However, with underdrive pulleys, the alternator may only spin at 2.5 to three times the crankshaft RPM's, if that. This isn't enough in typical stop and go traffic to keep your battery state of charge high enough nor to run you A/C blower, etc. The six to eight HP you may gain at the flywheel with under-drive pulleys diminishes to a three or four HP gain at the rear wheels considering typical drive train losses. Many people have come to the conclusion that the trade-off isn't very useful on a daily driver.

Have your battery fully charged and have a load test done on the battery. Assuming that it is OK (and I suspect that it is) then while the tester is hooked up to the battery, a load test can be done on the alternator (run the engine at about 4,000 RPM's with the underdrive pulleys installed). Most parts sales places will do this for free.

All my best,

Steve

[Blacky]

I put the pid on Paul recommended and its always with a little red dot and NO VOLTAGE :(

That should also be translated into an alternator fail light on your instrument cluster. Trust the intstrument cluster* befor trusting that PID - we have found some bit flags to be back to front.

* Assuming you have an alternator fail lamp and the lamp is functioning correctly.

Can anyone else log that PID to see if it reports correctly on a vehicle without a suspect alternator?

Regards
Paul

[PSWired]

I noticed that bit of the status PID was backwards the other day when I was logging on a 2002 GMC Yukon Denali.