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
• 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.