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Q: Bad alternator needs to be replaced.

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I think my alternator is bad. After charging the battery with a battery charger, it only reads 12.9 volts. The car only goes about 5 MPH at most and then die. Even when I jump the battery it only goes 5 MPH.

The alternator is not charging if voltage drops to below about 13.2 volts while the engine is running. If your car will not go over 5 MPH you may have other issues causing this like low fuel pressure or a computer issue causing the problem. The first thing a qualified technican should check is the charging and battery system. Then a computer scan and fuel pressure test if the charging system and battery are ok.

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