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ASE P2: Electrical System

By Larry Carley

Average battery life is only about four to five years, and sometimes less in hot climates.
The most commonly replaced electrical system parts include batteries, battery cables, alternators and starters.

Average battery life is only about four to five years, and sometimes less in hot climates. A new battery is needed when the battery can no longer hold a charge, or fails a load test or capacitance test.

A replacement battery must be the correct “group” size (same height, width, length and post configuration) as the original. Many GM vehicles use side-post batteries. Some replacement batteries have both top posts and side posts to fit a wider range of applications.

The “Cold Cranking Amp” (CCA) capacity of batteries will vary. The higher the CCA rating, the more cranking amperage the battery can provide for reliable cold starting. The “Reserve Capacity” (RC) rating is how many amp hours of operation the battery can provide should the charging system fail. A replacement battery should have CCA and RC ratings that meet or exceed the OEM battery requirements.

Conventional lead-acid car batteries are filled with a liquid acid electrolyte, but some use a “gel” electrolyte or “Absorbent Glass Mat” (AGM) construction with a paste electrolyte. AGM batteries are usually more durable, have a longer service life and hold a charge longer than conventional batteries, but cost more.
Batteries age in storage, so sell the oldest first and the newest last. Battery charge should also be checked prior to installation, and recharged as needed. Other parts that may be needed when replacing a battery include new battery cables, battery holddowns and battery tray.

The alternator produces current to meet the current requirements of the vehicle’s electrical system and to keep the battery fully charged. Charging output is controlled by a voltage regulator or the powertrain control module (PCM). An alternator that is not generating enough current or voltage may allow the battery to run down or go dead. Low output also can affect the functioning of onboard electronics and electrical accessories.

Alternators should be bench-tested to see if they meet specifications to reduce unnecessary warranty returns. If an alternator passes a bench test, the charging problem is due to something else (a wiring problem, voltage control problem, slipping drive belt, slipping OAD pulley or a bad battery).

Replacement alternators must have the same or higher amp rating as the original, and same mounting configuration. If an alternator has an “overrunning alternator decoupler” (OAD) pulley, the same type of pulley should be mounted on the replacement alternator.

A starter may have to be replaced if it fails to crank the engine. The problem may be a bad starter motor, a defective starter drive (which can be replaced separately on some starters) or an electrical fault (bad battery cables, ground straps or starter relay or solenoid).

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