The 6.7 Cummins has a reputation as a durable engine, and the problems owners most commonly report involve the emissions aftertreatment system (DPF, EGR, DEF and sensors), the variable-geometry turbocharger, and fuel contamination affecting the high-pressure fuel system. Each of these should be diagnosed by a qualified diesel shop and repaired, so the engine and its emissions equipment keep working as designed.
About the 6.7 Cummins
The 6.7 Cummins replaced the 5.9 in Ram heavy-duty pickups for the 2007.5 model year. It is a turbocharged, high-pressure common-rail diesel, and it has used a diesel particulate filter from the start; later trucks added selective catalytic reduction (SCR), which uses diesel exhaust fluid (DEF). For how it relates to the earlier engines, see 12 valve vs 24 valve vs common rail Cummins.
Commonly reported 6.7 Cummins problems
DPF clogging and regeneration issues
The diesel particulate filter traps soot and burns it off during regeneration. Owners commonly report frequent regenerations, warning lights and reduced power, particularly on trucks that make lots of short trips or idle for long periods, which can interrupt regeneration. A shop will check the related sensors and look for the source of excess soot, such as injector or EGR problems, before cleaning or replacing the filter by the manufacturer’s procedure.
EGR valve and cooler problems
Soot can cause the EGR valve to stick, and EGR coolers can clog or leak. Unexplained coolant loss is one of the symptoms commonly associated with an EGR cooler leak, and it needs prompt diagnosis.
DEF, SCR and NOx sensor faults
On trucks with SCR, faults in DEF quality, the DEF pump and heater, or NOx sensors are commonly reported. If they are left unrepaired, these warnings can lead to the truck limiting its speed.
Variable-geometry turbo sticking
The VGT adjusts its vanes to control boost. Soot buildup and actuator problems are commonly reported causes of sticking vanes, which show up as low power or boost-related codes.
Fuel contamination and injectors
Common-rail fuel systems are sensitive to water and debris in the fuel, which can damage injectors and the injection pump. Drain the water separator and change fuel filters on the schedule in your owner’s manual, and buy fuel from busy, reputable stations.
Emissions components are part of the engine’s design. The right fix for every fault above is diagnosis and repair, not removing or disabling equipment.
When does a 6.7 Cummins need a new engine?
Most of the issues above are repairs to components bolted onto the engine. Replacing the engine becomes the question when a shop finds internal damage, for example low compression, coolant in the oil, bearing failure, damage after severe overheating, or a piston damaged by a failed injector. A compression or leak-down test and an oil analysis help confirm what has happened inside.
If you do need a replacement, the choice is usually between a short block, a long block or a complete engine, which we explain in short block vs long block. We carry D&J 6.7 Cummins short blocks, long blocks and Ready Run engines listed by model-year range, along with 5.9 options, on our Cummins engines page, with the 6.7 options on our 6.7 Cummins engines page. Match the listing to your truck’s year and engine before ordering.
Related guides: 6.7 Cummins specs · CP3 pump · turbo failure symptoms · Cummins generations.
More guides: 68RFE problems · CP3 vs CP4 · 5.9 Cummins problems · diesel blow-by · diesel losing power · bad diesel injector symptoms · diesel black smoke · 6R140 problems (Ford Super Duty) · 5.9 vs 6.7 Cummins · how long a Cummins lasts · Cummins head gasket · 6.7 Cummins turbo actuator.
Trouble codes: P0087 Fuel Rail Pressure Too Low · P0299 Turbo/Supercharger Underboost · P0191 Fuel Rail Pressure Sensor Range · all OBD2 codes.
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