G3B, K3A and L3A Denso Alternators Caterpillar

Initial Troubleshooting Procedure

Usage:

426C 1CR

CHECK THE RESISTANCE IN EXCITATION CIRCUIT.

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Insert a 7X-1710 Multimeter Probe Group into the rear of the middle wire in the connector. See figure 1. Insert the probe (spoon lead) between the black seal that surrounds the wire and the outer shell of the connector. Do not insert the probe between the wire insulation and the black seal. This terminal (IG) is the terminal for excitation.

Read the voltage that is shown on the multimeter.
Expected Result: The voltage reads within .5 volts of battery voltage.
Results:
- YES - The voltage reads battery voltage. The excitation circuit is correct. Proceed to Step 2 .
- NO - The voltage is more than .5 volts less than battery voltage. There is a fault in the wiring harness to the alternator or there is a poor electrical connection. Correct the problem and operate the machine. Watch for a recurrence of the problem.

CHECK THE SYSTEM VOLTAGE.
1. Before starting the machine, connect a voltmeter between the "B+" terminal and the case of the alternator. Turn OFF all electrical loads.
1. Turn the key to the ON position but do not start the engine.
  Expected Result: This voltage should be system voltage.
  Results:
  - YES - The voltage is system voltage. Go to Step 3
  - NO - The voltage is less than system voltage. Verify that the batteries are good and verify that battery connections are good. Go to Testing and Adjusting, "T4 Alternator Drive System - Check" if the batteries are good.

INITIAL CHECK OF ALTERNATOR OPERATION.
1. The voltmeter remains connected in the configuration from Step 2 .
1. Start the machine. Set the throttle to at least 75%. Read the voltage on the voltmeter.
  Expected Result: The voltage is higher than the voltage recorded in the previous Step 2.
  Results:
  - YES - The voltage is higher than the voltage observed in the previous Step 2. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is charging partially. See the following diagnostic flow chart for reference in continued testing. Proceed to Testing and Adjusting, "T1 Alternator Output - Test" .
  - YES - The voltage is higher than the voltage observed in the previous Step 2. The voltage is also higher than the maximum voltage that is listed in the specifications for the alternator. The alternator is over charging. Proceed to Testing and Adjusting, "T8 Alternator Overcharging - Test"
  - NO - The voltage is not higher than the voltage observed in Step 2. Proceed to Testing and Adjusting, "T4 Alternator Drive System - Check" .