Voltage at battery 16+

[GBRandy]

For no reason I can point to, my 2001 Tundra Extended Cab V8 (Limited TRD) has developed a voltage issue I am struggling to correct.

I get 14.4 volts at the battery terminal until the car warms up. As it warms the volts at the battery terminal climb to 16 volts or more...the record being 16.9.

Pulled the alternator figuring it was the voltage regulator and went to have it rebuilt. The bench test showed 14.8 volts and 130 amps. I was stunned. They opened up anyway and the brushes are not even 20% gone. The voltage regulator was cleaned up and put back in and bench tested again with the same perfect result.

Thinking it may be a loose belt, I replaced the tensioner with a new Gates unit and the belt was swapped with a new Gatorback.

Up and running and the symptoms are still there.

Bought a brand new battery and slapped it in....same result.

Fearing rust on the grounding and frame, I added a ground strap from the engine block to the negative post on the battery...same result.

Gah. Now the car idles like crap and dies when I stop at a light (might just be the ECU relearn process here as the battery was out for a few days).

Truck has 91,000 miles and has been flawless (save for the rust recall) until this.

Any ideas on what to do next to fix this....besides take it to the dealer?

[RitcheyRch]

Very strange. All the issues you would see with a bad voltage regulator.

[Remmy700P]

The very LAST thing you should do is take this to the dealer. They employ parts swappers, not mechanics, so they don't know **** about diagnosis if it isn't in their "manual".

I'd suggest getting in contact with Kyle Cannon at DC Power. I'd bet he knows what the issue/fix is. His email: kyle@dcpowerinc.com

[GBRandy]

The very LAST thing you should do is take this to the dealer. They employ parts swappers, not mechanics, so they don't know **** about diagnosis if it isn't in their "manual".

I know. But I am beginning to feel the same way. I am half tempted to go buy a rebuilt alternator and put it in just becuase the symptoms are so strong.

I have owned this thing since new....and kind of perplexed.

[DJ]

The key to this is your statement:

"I get 14.4 volts at the battery terminal until the car warms up. As it warms the volts at the battery terminal climb to 16 volts or more..."

The difference between the alternator running in your vehicle and being tested on the bench is heat. I suspect the voltage regulator's reference climbs when it gets hot, and so the regulated voltage climbs with it. This happens in the vehicle as the vehicle warms up, but not on the bench, where the test is short and there is no external heat applied to it.

I suggest taking it back to where you had it tested and have them replace the voltage regulator with a new one. It's the least work, the least cost, and the most likely solution to the problem.

[GBRandy]

OK DJ.... I agree. I'll pull the darn thing out yet again.

[jack mccarthy]

FYI...

It's my understanding that the voltage regulators cannot be purchased separately and replaced. It was the case for the 2002 Tundra alternators when I thought I had a regulator issue and asked the local dealership parts guy. Generally they need a rebuild to get a new regulator with the core. I don't know about later model Tundras.

[silet]

The key to this is your statement:

"I get 14.4 volts at the battery terminal until the car warms up. As it warms the volts at the battery terminal climb to 16 volts or more..."

The difference between the alternator running in your vehicle and being tested on the bench is heat. I suspect the voltage regulator's reference climbs when it gets hot, and so the regulated voltage climbs with it. This happens in the vehicle as the vehicle warms up, but not on the bench, where the test is short and there is no external heat applied to it.

I suggest taking it back to where you had it tested and have them replace the voltage regulator with a new one. It's the least work, the least cost, and the most likely solution to the problem.

That's your answer!!! Once you go over 14.7 volts, the regulator is shot.

[GBRandy]

FYI...

It's my understanding that the voltage regulators cannot be purchased separately and replaced. It was the case for the 2002 Tundra alternators when I thought I had a regulator issue and asked the local dealership parts guy. Generally they need a rebuild to get a new regulator with the core. I don't know about later model Tundras.

I am blessed with a very good rebuild shop here in town (Green Bay Rebuilders). If the parts are available they will have it... Stand by, I will pull the unit out this weekend and drop it on Monday.

[Remmy700P]

That's your answer!!! Once you go over 14.7 volts, the regulator is shot.

No, that's not what it means.

When heat increases, the regulator increases the output voltage to compensate for increased resistance. If memory serves, every 1 degree change in temperature corresponds to a 0.1v change in output voltage. Note that it works the other way as well. Declining temperatures allow the regulator to decrease voltage while maintaining required amperage output.

[silet]

The regulator limits the charge to 14.7 volts. Anything more will eventually damage the battery. So your memory may be fine about the charge fluctuation, but not on the limit of the regulator. When you hit 16 volts, the regulator is not doing its job and you replace it.

[Yaesu]

Is the meter being used to measure the voltage defective? I cannot imagine removing the alternator and then removing the voltage regulator. I can't even see the alternator on my 2012 5.7 Tundra.

[GBRandy]

Meters...plural. I have three. Plus the one in the truck shows 3/4 high (or more) and fluctuates all over the place on the gauge.

Besides, removing an alternator is not that big of a deal. The darn skid plates are a headache and moving the PS pump out of the way is a pain, but seriously, all in? 2 hours to get it out...max.

You want fun? R&R the belt tensioner.....geez.

[GBRandy]

The regulator limits the charge to 14.7 volts. Anything more will eventually damage the battery. So your memory may be fine about the charge fluctuation, but not on the limit of the regulator. When you hit 16 volts, the regulator is not doing its job and you replace it.

...or hits 15 for that matter. Out it comes again

[jack mccarthy]

Be aware that the regulator can only regulate down to a certain load before it stops to regulate altogether. Doesn't mean the regulator is bad, it's just not operating within spec in order for it to function correctly. I had an issue with a dead cell in my battery that would cause the voltage to spike to 18-22V for the first minute until the RPMs cut back due to the heavy load. After that point it would begin to regulate at 14.5V even if I upped the RPMs. Thought it was the strangest thing until the alternator shop told me how they work.

I know the OP replaced his battery, so this would not be the issue as that is what fixed mine.