Alternator/charging issue

[Kyzrsoze]

I'm trying to diagnose a strange (to me) charging issue.

At idle I'm seeing 14v at the battery posts. While driving the battery warning light comes on every few seconds and the AC shuts on/off in response. I'm seeing a few codes related to low voltage.

Has anyone seen an alternator fail this way? My expectation would be low voltage at idle and improvement while driving. This is reversed.

The car is a 2006 Lexus GS.

 

[torinodan]

Only seen this on the vehicles that turn off the alternator for mpg's while driving. Wife's Nissan did that. Battery died all the time while we drove. I discovered the wire that turned off the alternator wife driving. I removed it from the connector. No more dead battery and no change in mpg. I'm happy and for her suv that was dumb.

 

[BH-ATL]

Year ago one of the diodes that turned the AC from the alternator to DC was bad on my BMW . It would read 13+ voltage but not enough amps to really run anything.

 

[joel2000]

Had it happen on my 97 250 w/ 7.3.
13.8 - 14.2 vdc at idle and battery light flash on occasion at highway speed. Alternator….

 

[Kyzrsoze]

Appreciated, Good feedback all.

I'd prefer it be a bad alternator over chasing down wiring issues.

 

[torinodan]

Mine probably is a bad alternator or it's the computer. Easier for me to unplug the wire and fix a solution for a problem that never existed.

 

[Jambo]

What's the mileage? The Denso in my 1989 Toyota went out at about 250,000 miles. When it failed it turned on the "charge" and "brake" lights simultaneously. It was still producing voltage according to the gauge, but not enough amperage because the slip rings had worn out.

In your car the electric cooling fan likely comes on with the A/C, and that's a pretty high amperage draw. The computer may be turning the A/C off because the fan isn't running properly. It depends on how much the computer controls and "sees" I guess.

 

[Lobo1]

You either got a diode going out or the voltage regulator is. Both are internal inside the alternator unless you got an older vehicle that has the voltage regulator mounted on the firewall.

 

[ARCman47]

Appreciated, Good feedback all.

I'd prefer it be a bad alternator over chasing down wiring issues.

Definitely possible. I know on my 6.0 Powerstroke, the "battery light" will flash because of alternator, NOT because of battery voltage which is confusing as hell 🤣

 

[laserbeam1k]

Random question. You got a Transmission issue yet? I think that Transmission is the 6 speed auto and is known to have issues. Also I had a 06 Is250 same transmission. Had to change out the alternator 3x times. The one from Autozone although had a lifetime warranty, went out on me twice. Id get an original Denso if you can.
And you can also take the alternator off the engine and have some Autozones bench test it.