7. Battery Diagnostic Procedures

(USING LOAD TESTER VAT40 or equivalent)

1. Start engine and confirm that alternator warning light is not illuminated.

NOTE:
If the warning light is illuminated, the self-diagnostic function is operating. Check the alternator and related harness. Refer to the instructions - in section G of the applicable workshop manual.

2. Check the alternator belt tension and condition.

3. Turn the vehicle headlights "ON". Check engine belt and alternator bearing for unusual noise by raising and lowering the engine RPM.

4. Turn ignition and all accessories "OFF".

5. Connect a load tester.

6. Apply the load test referring to the table (refer to Charging and Load Testing Information) and flow charts on 7 or 7a., Battery Diagnostic Procedures (depending on the test equipment). The final voltage must be above the minimum value shown in the table. Record the voltage on the "Battery Check Sheet".

^ If the voltage is more than the minimum, measure the open circuit voltage. Charge the battery if less than 12.4V.

^ If the voltage is less than the minimum, "quick or "boost" charge the battery for 30 minutes.

CAUTION:
DO NOT "Quick" or "Boost" charge MX-5 Miata batteries. These batteries are gel type and must NOT be charged at more than 20 amps.

^ Perform a load test again. If the battery is still below the minimum voltage, replace the battery and proceed to step 8.

7. Start the vehicle and raise the RPM to 2500.

8. Connect the battery load tester and apply a load equal to the alternator rating.

^ If the voltage is 13.5V to 15.0V, the alternator and battery are functioning correctly.

^ If the voltage is more than 15.0V, replace the alternator.

^ If the voltage is 13.5V or under, check for resistance between the battery and terminals "B and "S". Inspect the harness for damage. Repair as necessary. Retest the alternator. If the voltage is still less than 13.5V, replace the alternator.

IMPORTANT
Diagnostic procedures for lead-acid battery performance are different than those used for maintenance-free batteries (lithium hybrid type). Incorrect diagnosis will result in false readings and unnecessary battery replacement if the wrong procedure is followed.

Use "Flow Chart"





Diagnostic procedures used for testing lead-acid batteries provide false readings leading to unnecessary replacement if used on maintenance-free batteries. The information below is provided for diagnosing maintenance-free batteries.

*CAUTION:
DO NOT BOOST OR QUICK CHARGE MX-5 MIATA "GEL-TYPE" BATTERIES.