Voltage Regulator question(s)

[carlajean42]

Hi all! I found this forum because of searching for battery light issues in my 07 Yaris. I'm not going to bother running down all the problems and differential in detail but I'll list them briefly below.


Battery light on
Replaced battery (after diagnostic)
Replaced serpentine belt (it was worn)
Battery light still on
Alternator in-car test and bench test passed just fine :iono:
Suspect voltage regulator


Yes, I know the above are very typical to the other threads, and I have read them. However, after searching/reading through I didn't find the answers to the below so I appreciate the help.

Here are my main questions:

Would a bad voltage regulator allow an alternator to pass a bench test (diagnostic)?
What is the advantage of replacing just the voltage regulator (if bad) vs. just replacing the entire alternator?


Thank you for your help.
:headbang:

[nortonfb]

Only if it's an intermittent problem.
The advantage is that it's cheaper.
From experience, check the horn fuse underneath the hood. The cover of the fuse box
gives position. 7.5 amp fuse.
Norton

[nookandcrannycar]

??? I thought replacing the voltage regulator isn't done because (re the location) it doesn't make financial sense...might as well get a rebuilt one that meets OEM specs.

[Bluevitz-rs]

I believe 2007 was the year of the bad regulator problem. I was allowing water inside the regulator causing it to fail intermittently and causing the light to come on, but the voltage would check out fine until complete failure. Just replace it from another car of a newer year.

[IllusionX]

I believe 2007 was the year of the bad regulator problem. I was allowing water inside the regulator causing it to fail intermittently and causing the light to come on, but the voltage would check out fine until complete failure. Just replace it from another car of a newer year.


That's interesting. I never had issues with my 07, BUT my alternator was replaced in 08 at 55000km under warranty because it was making noise. I have had my 07 since October 2006...

[CrankyOldMan]

My wife's 07 sedan had its alternator go tits up this past summer. Found an 09 at the local salvage yard, no further problems.

[CTScott]

I believe 2007 was the year of the bad regulator problem. I was allowing water inside the regulator causing it to fail intermittently and causing the light to come on, but the voltage would check out fine until complete failure. Just replace it from another car of a newer year.

Correct - There is a TSB on this. You can replace just the regulator, but often a used junkyard alternator from an 08 or newer is cheaper than the regulator.

Typically when the regulator fails, it does so reliably, so the alternator should fail a bench test.

The 7.5Amp fuse mentioned above is the ALT-S fuse in the under-hood fuse panel. That fuse feeds the regulator with a reference voltage from the battery. If it is popped the alternator will not work correctly in the car, but will work perfectly on the bench.

[nortonfb]

The only symptom I had was the battery light. I had the voltage regulator and battery tested, just to double check my own test. I was afraid of being stranded and bought a used alternator (2012) from a wrecker for less than $40.
Actually found the fuse by accident, thanks to something CT had mentioned.
Now that I have a alternator back up, I'm sure the original one will never fail...
Norton

[nookandcrannycar]

The only symptom I had was the battery light. I had the voltage regulator and battery tested, just to double check my own test. I was afraid of being stranded and bought a used alternator (2012) from a wrecker for less than $40.
Actually found the fuse by accident, thanks to something CT had mentioned.
Now that I have a alternator back up, I'm sure the original one will never fail...
Norton

Wow, that's cheap. After reading Scott's post #7, I was going to reply with the question...Which is cheaper, a rebuilt alternator (remanufactured?) or one from a wrecker/junkyard? Your post answered my question. I was either in Missouri or Iowa (on my way to the Twin Cities) in 2010 when I could tell, re how my '07 was performing, that either the battery or the alternator was starting to fail. I had replaced the battery a bit over 20,000 miles before that, so I didn't think it was the battery. I barely made it to Burnsville, MN (Twin Cities metro, south side). I stopped by the Toyota dealer there and they wanted between $600-700 for a new alternator...just the part. There was a Sears in a shopping center on the other side of the freeway. I went to Sears...and I also barely made it there. The service writer called around to different suppliers. Only one place had any, and they only had one. He said 'They do the best job (I forget what term he used...rewinding? rebuilding? remanufacturing?), so if only one is available I'm glad it is their work'. The cost was about an even $300 including installation. It's still in the car 4 3/4 years and 140,000 or so miles later.