[faridhaddad]

Hi every one
In my impala 2000 the altenator started to give 17.5 volts instead of 13.5 volts .
I have changed the altenator 3 times and the problem still exicet, nothing changed .
Is there any body knows how can i reduce that voltage .
Thanks to every one

[Ricky Rocket]

Have you checked to see if there are any trouble codes? I am guessing that the ECM is involved in the charging system and it may be giving you some problems.

Rick

[lakota]

Altenators can and will put out 16.5-17.5 volt if you take a reading at the output lug. If you take that same reading at the fuse box, it will probably read 12.5-13.5. When altenators increase the current to charge the battery, the voltage goes up with it. If you've just started your car and then take a reading, it will read higher than normal. It's putting back what the starter just took. Take a reading after you've been running for a while. It should read 13.5-14 volts at the altenator, and 12.5-13 volts at the fuse box. On the plug that goes into the side with two wires coming out of it, one wire goes to your fuse box. This wire is the sensor for the altenator. If the voltage drops at the fuse box, this wire will cause the altenator to increase voltage/current to get the battery back up to normal voltage. If this wire is broken, bad connection, or short, the sensor reads less than 12 volts and the altenator increases voltage and amperage and will hold it there. You've replaced your altenator 3 times, the problem is not in your altenator. Look for a light or other electrical item that doesn't work, it may be shorting out, giving the sensor a false reading. Read the votage at the 2 wires in the plug, one should be 12.5 volts, the other should be a volt higher. Have your battery checked, sometimes we tend to overlook the most obvious. It could just be dirty post connections or a bad cell.

[TechnTool]

A common problem that causes this symptom is a bad battery. What is the open voltage of the battery? If it has a dead cell, then the Alt will work overtime trying to charge it.