Cummins
Cummins fault code
SPN 638 / FMI 7
Cummins Fault Code 173: Rack Actuator - mechanically stuck open
173 on Cummins engines means: Rack Actuator - mechanically stuck open. The failure mode (FMI 7) is “mechanical system not responding or out of adjustment”.
Lamp: Yellow
Engine may continue to run, but must be repaired the same day.
Code details
- Manufacturer
- Cummins
- Applies to
- Cummins QS-series electronic engines
- Fault code
- 173
- J1939 SPN
- 638
- FMI
- 7 — Mechanical system not responding or out of adjustment
- J1587 PID / SID
- S023
- Engine models
- QST30
What to do next
- Read active and inactive codes with the OEM service tool and note the occurrence count.
- FMI 7 tells the shop the type of failure to test for: mechanical system not responding or out of adjustment.
- Have a heavy-duty diesel technician confirm the fault against the engine or chassis service manual before replacing parts.
Get this code diagnosed
Send one request and nearby diesel shops and mobile mechanics can quote the repair.
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Related fault codes
Source: Cummins "Diagnostic Fault Codes For Cummins Engines", publication 80-1044 Rev 5/2013, page 4. See also OBD-II codes.