Caterpillar — Rotating Rectifier - Test

Testing & diagnosis

From a Caterpillar owner's manual covering: 3306B, 3406, 3406E, 3412C, SR4B. Check it applies to your exact model before use.

Applies to: Caterpillar 3306B, Caterpillar 3406, Caterpillar 3406E, Caterpillar 3412C, Caterpillar SR4B

Procedure

1. Touch the red ohmmeter lead to the rectifier terminal marked '+'.
2. Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
3. Touch the black ohmmeter lead to the rectifier terminal marked '+'.
4. Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
5. Touch the black ohmmeter lead to the rectifier terminal marked '-'.
6. Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
7. Touch the red ohmmeter lead to the rectifier terminal marked '-'.
8. Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
9. If the meter does not indicate the expected result, the rectifier is bad. Replace the rectifier.

Full service-parts list: Caterpillar 3406 →, Caterpillar 3406E →, Caterpillar 3412C →, Caterpillar SR4B →

Source: Caterpillar owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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