Aftertreatment DOC Outlet Temperature Rate Abnormal
What does CUMMINS-3768 mean?
The CUMMINS-3768 (Cummins) diesel fault code means: Aftertreatment DOC Outlet Temperature Rate Abnormal. This is a moderate severity code.
Common Symptoms
- DPF lamp illuminated on dash
- Active regeneration messages on dash
- Increased backpressure and reduced power
- Higher than normal fuel consumption
- Black smoke out of stack when accelerating
Probable Causes (Ranked by Likelihood)
- DPF severely loaded with soot requiring forced regen Very Likely
- Excessive ash accumulation (cleaning required) Likely
- Failed differential pressure sensor or hoses plugged Likely
- Short-trip duty cycle prevented passive regen Possible
- Faulty DOC (upstream oxidation catalyst) Possible
- Aftertreatment fuel injector stuck or clogged Less Likely
Step-by-Step Diagnostic Procedure
Connect INSITE and read soot load estimate, differential pressure, and last regen status for fault 3768.
Park truck safely in non-combustible area with parking brake and initiate a parked/forced regeneration via INSITE.
If forced regen fails or DPF is above 100% soot load, remove DPF for professional cleaning (ash + soot bake).
Inspect differential pressure sensor hoses at DPF for soot clogging or kinks -- replace if obstructed.
Verify DOC inlet temperature rises above 570 degrees F during regen command (DOC functional check).
Inspect aftertreatment fuel doser or dosing injector for clogging; clean or replace as needed.
Common Fixes by Vehicle
What techs usually find when diagnosing CUMMINS-3768 on specific diesel vehicles:
EGR differential pressure sensor - the tubes going to the sensor plug with soot and carbon, so the ECM sees an unrealistic delta-P. Remove the two 5/16 steel lines, clear them with a torch and carb cleaner, and replace the sensor. Use OEM Mopar to avoid early failure.
If the sensor and tubes are clean, the EGR cooler bypass valve or the EGR valve itself is stuck, creating abnormal pressure readings. Command the EGR valve with Insite while watching flow - if it doesn't respond linearly, replace the valve.
Frequently Asked Questions
What is Cummins fault code 3768?
Cummins fault code 3768 indicates: Aftertreatment DOC Outlet Temperature Rate Abnormal. It is a moderate-severity fault in the aftertreatment or emissions system.
Can I drive with Cummins fault code 3768?
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 3768?
Repair cost is approximately $500-$2,000 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.