Aftertreatment SCR System - Fault Severity 1
What does CUMMINS-2641 mean?
The CUMMINS-2641 (Cummins) diesel fault code means: Aftertreatment SCR System - Fault Severity 1. This is a critical severity code.
Common Symptoms
- Engine protect mode or forced shutdown
- DEF warning lamp illuminated
- Countdown to engine derate (typically 50 hours)
- Low DEF or poor DEF quality warnings
- SCR efficiency drops (NOx emissions up)
- Possible 5 mph limp mode if ignored
Probable Causes (Ranked by Likelihood)
- Contaminated or watered-down DEF Very Likely
- Failed DEF pump or dosing module Likely
- Clogged DEF doser nozzle (urea crystallization) Likely
- Failed DEF quality or level sensor Possible
- DEF tank heater failed (frozen DEF) Possible
- Corroded DEF supply module harness Less Likely
Step-by-Step Diagnostic Procedure
Connect INSITE and verify DEF pump pressure builds to spec (around 70-130 psi) during dosing test.
Check DEF quality with a refractometer -- must read 32.5% urea concentration. Replace contaminated DEF.
Inspect DEF doser nozzle tip for urea crystallization -- clean with distilled water, do not use solvents.
Measure DEF tank level and temperature via INSITE; replace failed temp or level sensor if erratic.
Inspect DEF supply lines for kinks, leaks, or crystallization at joints.
If pump fails dosing test for 2641, rebuild or replace DEF pump module and reprime the system via INSITE.
Frequently Asked Questions
What is Cummins fault code 2641?
Cummins fault code 2641 indicates: Aftertreatment SCR System - Fault Severity 1. It is a critical-severity fault in the aftertreatment or emissions system.
Can I drive with Cummins fault code 2641?
Short-term, yes, but the engine will enter derate (typically starting at 55 mph and progressing to 5 mph for emissions faults). Drive directly to a repair facility. Do not defer this fault more than a few operating hours.
How much does it cost to fix Cummins fault 2641?
Repair cost is approximately $500-$3,500 including parts, labor, and any dealer programming required. DIY repairs (sensor replacement) fall at the low end; pump, aftertreatment, or ECM work falls at the high end and usually requires INSITE diagnostic software.