Cummins/Onan — Testing Control Board A1
Testing & diagnosis · Control printed circuit board A1
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Short circuiting battery cables can cause severe personal injury; disconnect negative cable before servicing
Procedure
- Disconnect the negative (-) battery cable.
- Remove the control box cover and separate it from control board A1.
- Check continuity across each P1/J1 and P3/J3 connector; replace corroded or resistive sockets.
- Reconnect the battery and try to start and run the set.
- If the engine does not crank, measure voltage at connector P1-2 while pressing the start switch.
- If the engine cranks but does not start, measure voltage at connectors P3-3 and P3-6 while cranking.
- Replace control board A1 if the voltmeter indicates zero volts at the applicable connector.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- At least 9 volts indicates the control board is not the problem
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.