Cummins/Onan — Testing Diodes (CR1 thru CR6)
Testing & diagnosis · Rotating exciter diodes
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan DFM
Before you start
- Excessive dust or dirt on diodes causes overheating and eventual failure; keep assemblies clean
Procedure
- Remove one diode at a time from heat sink; test and reinstall before next
- Check resistance with an ohmmeter, one lead to top of diode, other to diode stud
- Reverse leads and observe reading again
- A good diode has higher reading in one direction than the other; if both high or both low it is defective
Tools required
- Ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Good diode: high resistance one direction, low the other
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.