Cummins/Onan 3.6MKY / 4MKY — Field Voltage Test
Testing & diagnosis · Voltage regulator / generator
For the Cummins/Onan 3.6MKY / 4MKY, from the Cummins/Onan service manual.
Applies to: Cummins/Onan 3.6MKY, Cummins/Onan 4MKY
Before you start
- Attach and remove meter leads only when genset is not operating.
Procedure
- Test A: Connect DC voltmeter positive to J4 pin 7 and negative to J4 pin 3.
- Push start switch; approximately 12 VDC indicates field flash voltage is available; proceed to Test B.
- Test B: Move positive lead to pin 9 and negative to pin 10; start the genset and allow speed to stabilize.
- Measure field voltage no load then full load; 40 VDC no load to 100 VDC full load is normal.
- Test C: Disconnect J4 from P4, attach AC voltmeter to L1 and L2, and apply 12 VDC to P4 pins 9 (+) and 10 (-).
- Start the genset; approximately 40 VAC indicates brushes, rotor and stator are OK.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 12 VDC field flash
- 40-100 Amazon eBay KuduParts $67.00 FridayParts $68.90 VDC field voltage
- approximately 40 VAC in Test C
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.