Cummins/Onan — Rack Position Fault/Test Procedure
Testing & diagnosis · Governor output module (A38)
From a Cummins/Onan service manual covering: 1000DFHD-60 / 900DFHD-50, 750DFHA-60 / 620DFHA-50, 800DFHB-60 / 700DFHB-50, 900DFHC-60 / 800DFHC-50. Check it applies to your exact model before use.
Applies to: Cummins/Onan DFHA, Cummins/Onan DFHB, Cummins/Onan DFHC, Cummins/Onan DFHD, Cummins/Onan QST30 engine, Cummins/Onan QST30-G1 engine, Cummins/Onan QST30G2 engine, Cummins/Onan QST30-G3 engine, MTU QST30G3 engine
Procedure
- Move the Run/Off/Auto switch to the Off position.
- At the engine interface board (A31), place a jumper wire from A31-TP1 to A31-TP2.
- Select RACK TEST from the Setup Menu to initiate the fuel rack test.
- Verify A38 DS1 (RUN) and A38 DS2 (VCC) LEDs are on; if not, remove jumpers, restart set and troubleshoot.
- Check whether fuses A38 F1 and F2 are blown; replace blown fuse and restart set.
- Move both racks from 0mm to 19mm from the POS MM menu and read DC volts from J11-B and J11-C to J11-A.
- Verify these voltages correspond to the display (± .25 VDC).
- Check if both left and right voltages are out of tolerance.
- Move the racks to 0mm and monitor the position voltage of the incorrect side.
- Disconnect the fuel pump connector; check if voltage rises from approximately 1.3 ±.25 VDC to 4.5 ±.25 VDC.
Tools required
- Calibrated RMS multimeter (Fluke 87 or 8060A) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Engine Torque Adjustment procedure must be performed after replacement of fuel pump or governor output module
Full service-parts list: Cummins/Onan DFHA →, Cummins/Onan DFHB →, Cummins/Onan DFHC →, Cummins/Onan DFHD →
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.