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Alternator Voltage High

98 Nissan Sentra with 240K miles on it, very well maintained. The alternator is only three years old, but is now putting out over 16 volts, agreeably bad.

Is there anyrepair/replacement possible of the internal regulator?

It can be done but it is usually better to just replace the alternator with a remanufactured unit I feel.

Be sure you are getting the correct voltage reading, measured at the battery, with a known good meter. Do NOT start buying parts on the strength of a dashboard meter reading…

I looked at the manual for a 98 maxima alternator, which I assume is similar to yours. The regulator replacemet doesn’t look to be too bad of a job.

I’m not sure from the drawing if the front pulley is held on with a nut or pressed on to the shaft. If it is pressed on, you need special equipment to remove and install it.

Be sure to check the connection between the main output lead of the alternator and the battery positive cable. A disruption in this circuit can cause an artificically high voltage reading.

Many vehicles use a fusible link in that circuit so a blown link is something to consider.
If there is a problem in the alternator/regulator then the entire unit should be replaced.