Cummins/Onan — Alternator Checkout (C)
Testing & diagnosis · battery charging alternator
From a Cummins/Onan service manual covering: DL4, DL6, DL6T. Check it applies to your exact model before use.
Applies to: Cummins/Onan DL4, Cummins/Onan DL6, Cummins/Onan DL6T
Procedure
- With engine running, check the battery charge rate DC ammeter; it should show a slight charge tapering to zero.
- If constant discharge or constant high charge, stop set and check drive belt, terminal connections, and lead wires.
- Use a voltmeter between output terminal and ground; nominal output should be 13.8 to 14.8 volts.
- If output high (over 15 volts), check for loose or corroded voltage regulator leads; replace regulator if shorted.
- If output low, problem could be worn/broken brushes, open regulator, or open field diode.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Nominal output voltage 13.8 to 14.8 volts
Full service-parts list: Cummins/Onan DL6 →
Source: Cummins/Onan service 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.