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Electrical System

Troubleshooting the Alternator and Vehicle Charging System

Note: The following instructions listed below consist of general information for troubleshooting the alternator and vehicle charging system. Refer to the Original Equipment Manufacturer's service manual for specific information pertaining to your vehicle.

 

FIRST, IF AVAILABLE, CONDUCT AN ALTERNATOR PERFORMANCE TEST WITH AN ALTERNATOR/STARTER TEST BENCH.

  • If the alternator is not charging, it is important to resolve any additional vehicle side problem(s) in the charging system that may have an effect on the alternator.
  • If the alternator meets the manufacturer's specifications, refer to the manufacturer's service manual to inspect the vehicle charging system and to identify the problem(s) and possible corrective action(s).
  • If an alternator/starter test bench is not available, identifying the customer's true charging system problem is important to prevent unnecessary alternator replacement. Troubleshoot the system with the following questions:

1. DOES A CHARGE LAMP, AMPERAGE (AMP) GAUGE OR VOLTMETER INDICATE A CHARGING SYSTEM PROBLEM?

  • Charge lamp: A low idle can cause the alternator light to illuminate dimly. A weak battery can cause the alternator light to illuminate during high amperage draw. Corroded, broken or frayed wires/connections could cause the alternator light to illuminate during idle. Note: Some charging systems will not properly operate if the charge lamp bulb fails.
  • Amp gauge: Broken, loose or frayed wires/connections could cause erratic readings on the gauge.
  • Voltmeter: Gauge readings should be between 12.0 and 12.6 volts with the ignition on and the engine not running. Lower readings could indicate a low battery, poor connectors or broken wiring. Gauge readings should be between 13.2 and 14.5 volts with the ignition on and the engine running. Higher readings could indicate a failed regulator or poor wiring connectors and a lower reading could indicate a failed alternator or poor wire connections.

2. IS THERE A FUSE OR FUSIBLE LINK IN THE CHARGING SYSTEM?

  • Check the Owner's manual or manufacturer's service manual for location and usage.

3. IS THE BATTERY FULLY CHARGED? HAS IT BEEN LOAD TESTED?

  • The battery must be fully charged (12.6 volts) and the battery cables and terminals in good condition.

4. IS THE ALTERNATOR BELT TENSION WITHIN THE MANUFACTURER'S RECOMMENDED SPECIFICATION AND IN GOOD CONDITION (NOT CRACKED, GLAZED OR CUT?) NOTE: THE CONDITION OF THE ALTERNATOR DRIVE BELT IS CRITICAL TO ALLOW THE ALTERNATOR TO ACHIEVE MAXIMUM CHARGING UNDER LOAD. (IF ANY OF THE AFOREMENTIONED CONDITIONS APPLY, THE CUSTOMER SHOULD REPLACE THE DRIVE BELT.)

  • If the belt is too loose, it can cause the alternator to charge irregularly or not at all.
  • If the belt is too tight, damage to internal bearings will cause premature failure of the alternator.
  • If the belt is worn or too narrow it will slip around the pulley, causing irregular charge to the battery.
  • The break-in period for a new belt is approximately 10 minutes. It is very important to verify and retighten the belt tension to the manufacturer's specification after the initial 10 minutes of operation.

5. HAS THE WIRING BEEN CHECKED FOR DAMAGE, LOOSE CONNECTIONS AND FRAYED BATTERY CABLES? HAVE THE TERMINALS BEEN CHECKED FOR CORROSION?

  • The battery must be fully charged (12.6 volts) and the battery cables and terminals in good condition.

6. HAS THE VEHICLE BEEN MODIFIED OR HAD ADDITIONAL EQUIPMENT INSTALLED AFTER IT LEFT THE FACTORY?

  • Excessive non-factory accessories such as phone or computer outlets, televisions, refrigerators, stereo equipment/systems or lights can overburden the alternator performance and cause premature failure.
  • Improper installation procedures of the aforementioned accessories including poor ground points, loose connections or improper wiring may cause charging problems.

7. HAS THE ENGINE OR TRANSMISSION BEEN MODIFIED OR REPLACED? QUITE OFTEN, VEHICLES WITH THE AFOREMENTIONED REPAIRS WOULD EXPERIENCE ELECTRICAL PROBLEMS, DUE TO A MISSING GROUND WIRE OR POOR CONNECTION.

  • Check the ground circuit between the battery and the engine for high resistance.
  • Verify the vehicle has two good electrical ground points, one from the battery to the engine and the other from the firewall to the frame.
  • The circuits for today's applications have separate ground points, however, older applications may not. Please refer to the manufacturer's service manual.

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