Alternator overcharging 29 volts

  • 1992 SAAB 900
  • 2.0L
  • 4 CYL
  • 2WD
  • 158,000 MILES
Alternator is putting out 29 volts it was replaced about 5,000 miles ago.
Do you
have the same problem?
Thursday, February 25th, 2021 AT 12:06 PM

1 Reply


The voltage regulator on this vehicle is internal within the alternator. If you are getting 29v, it certainly will burn things up. I would not drive it until it's repaired.

Here is what I suggest: Remove the alternator and have it bench tested at a local parts store. That way we can confirm that is the issue. However, there really isn't anything else that would cause it other than the alternator/regulator.

If it was replaced recently, chances are it should still be under warranty.

I don't know if you need them, but here are the directions for removal and replacement. First, here is a link that shows in general how one is replaced. You can use it as a guide.

Here are the directions specific to your vehicle. The attached pics below will correlate with the directions.


1992 Saab 900 L4-1985cc 2.0L DOHC Turbo EFI
Replacement of Alternator
Vehicle Starting and Charging Charging System Alternator Service and Repair Procedures Replacement of Alternator
Removing/Installing Alternator

1. Disconnect the negative (-) battery cable.

pic 1

2. Loosen the alternator V-belt tensioning bolts, pivot the alternator and remove the alternator V-belts.

3. Remove tensioning bolts.

4. Disconnect the wires from the rear of the alternator.

5. Pivot alternator away from block to allow access to alternator bracket mounting bolts.

pic 2

4. Remove the alternator bracket mounting bolts and the alternator.

Note: The alternator bracket must be removed with the alternator to allow removal of the pivot bolt.

6. Install the new alternator, leaving the tensioning bolts slightly loose. Install the V-belt and tension it.

CAUTION! V-belt tension is critical to the life of alternator and proper alternator operation. A loose belt will cause undercharging (and often a loud screeching sound). A tight belt will quickly destroy the alternator bearings and the bearings of other components driven off the same belt.

7. Tighten all tensioning bolts. Install the wiring to the alternator. Reconnect the battery terminal and check the operation of the charging system warning lamp.

Note: Be sure to reinstall the insulating boots to the wire terminals on the back of the alternator.


Remember, if you are producing that much voltage, it can cause damage and even cause a fire, so it needs attention.

Let me know if this helps or if you have other questions.

Take care and God Bless,

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Thursday, February 25th, 2021 AT 6:46 PM

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