Cummins fault code 1921 is the Cummins Aftertreatment Diesel Particulate Filter Differential Pressure – Data Valid But Above Normal Operating Range – Moderately Severe Level document for the ISX11.9 CM2250 (2010-12) engine platform, a 9-page PDF that reproduces the official fault code write-up read with Cummins INSITE. The engine estimates soot load in the aftertreatment diesel particulate filter from the differential pressure sensor and the calculated soot output, and under light duty cycles the filter may not reach the temperature needed to regenerate.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISX11.9, ISX15, ISB6.7, ISC8.3 and ISL9 CM2250 |
| System / group | ISX11.9 CM2250 (2010-12) / DTCs |
| Fault code | 1921 — PID S324, SPN 3251, FMI 0/16 |
| Warning lamp | Amber |
| Publication reference | Cummins troubleshooting bulletin 2883445 (aftertreatment differential pressure sensor circuit) |
| Pages | 9 |
| File size | 0.2 MB |
| Format | |
| Language | English |
What Cummins fault code 1921 means
It sets when the ECM detects the soot load has exceeded the moderately severe recommended limit while engine speed is above 500 rpm. The amber lamp illuminates, the aftertreatment dash lamp flashes, the EGR valve closes and the engine enters a protection derate. The document walks a technician through the summary and the guided troubleshooting steps needed to confirm and clear the code.
Document table of contents
- Overview and circuit description
- Component location
- Conditions for running the diagnostics
- Conditions for setting the fault code
- Action taken when the fault code is active
- Conditions for clearing the fault code
- Shop Talk and possible causes
- Associated procedures and guided troubleshooting steps
Applicable truck models
This troubleshooting document covers Cummins ISX11.9, ISX15, ISB6.7, ISC8.3 and ISL9 CM2250 engines in Class 6 to 8 trucks. It is filed under the ISX11.9 CM2250 (2010-12) / DTCs group and also applies to ISX12 CM2250 installations, so confirm the engine dataplate before ordering parts. Cross-reference the calibration revision with Cummins official engine support before clearing the code.
Who needs this Cummins fault code 1921 manual
Heavy-duty diesel technicians, fleet maintenance teams and workshop owners diagnosing a moderately severe DPF soot-load derate use this reference to read SPN 3251 / FMI 0/16 correctly and to follow the guided steps in INSITE. The possible causes it lists include:
- a duty cycle too light to actively regenerate the filter
- exhaust temperatures too low to burn off trapped soot
- a plugging or malfunctioning diesel particulate filter
The full 9-page PDF for diesel particulate filter fault code 1921 is available in the DiagTechPro manuals library; a free account is required to download.
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