Dodge and Ram Cummins Repair, 5.9 12‑Valve to 6.7
Cummins repair on a Dodge or Ram depends on which era of engine sits under the hood, because a 12-valve with a mechanical P7100 pump fails nothing like a 6.7 with a CP4 and a DEF tank. We work on all of them and tell you what needs fixing now and what can wait.
Start with the engine size, then narrow it down
Every Ram heavy-duty diesel since 1994 is a Cummins inline six, a 5.9 or a 6.7.
The model year settles it, except on 2007 trucks, which came with either engine depending on build date. Jump to the year picker.
Six Cummins eras and what each one brings in for
Pick your years.
5.9 12-valve with the Bosch P7100
A mechanical inline pump and no computer running the fuel. Leaks, worn injectors and tired front ends outnumber pump trouble. Our diesel injection pump repair page covers how the P7100 is checked.
- Hard starting when cold
- Oil and fuel leaks
5.9 24-valve with the VP44
This electronic rotary pump depends on the lift pump for steady supply, so we test supply pressure before condemning it.
- Stalling or dying at idle
- Hard start after it sits
5.9 common rail with the CP3
A Bosch CP3 feeds a common rail and electronically fired injectors, still with no EGR or DPF. Injectors wear at high miles. See diesel injector repair for how we test them.
- Rough idle or a miss you can feel
- Lost pulling power
Early 6.7 with EGR, DPF and a NOx adsorber
A CP3, a variable-geometry Holset, EGR, a DPF and a NOx adsorber. A plugged filter usually has a reason upstream. Start with DPF repair.
- Regens that run constantly
- Reduced power after an emissions code
6.7 with SCR and DEF
From 2013 the pickups added SCR and diesel exhaust fluid, still with a CP3 and, on most trucks, a 68RFE six-speed. DEF heaters, pumps and NOx sensors start to fail. See DEF system repair.
- DEF warning or a countdown on the dash
- Transmission heat when towing
Current 6.7 with the CP4
Ram used a CP4 pump on 2019 and 2020 trucks, which has little patience for water or poor fuel. Standard-output trucks from 2025 run a ZF eight-speed.
- Hard start or a stall with fuel pressure codes
- Shift complaints on newer transmissions
Same complaint, different suspects on a 5.9 and a 6.7
A starting point. Testing decides.
| What the truck does | Usual suspects on a 5.9 | Usual suspects on a 6.7 |
|---|---|---|
| Hard start or no start | Lift pump, VP44 on 24-valves, grid heater, air in the fuel | Fuel pressure, CP3 or CP4, grid heater, sensors |
| Low power or limp mode | Fuel supply, injection pump, boost leaks | Clogged DPF, sticking turbo vanes, EGR faults, DEF derate |
| Smoke or a miss | Worn injectors, timing on mechanical pumps | Injectors, EGR, turbo oil seals |
| Slipping or flaring shifts | 47RH, 47RE or 48RE, fluid, pressure and heat | 68RFE, Aisin or ZF, fluid, wiring and heat |
That is our kind of problem. Diesel diagnostics traces the code to the part that set it, including on trucks other shops could not sort out.
On the road with two options and a clear answer
From Google, word for word.
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- Customer
- Kenbob
- Trip
- Traveling through to Utah
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The repairs Cummins owners bring us
The engine lasts. The parts bolted to it fail.
Pumps and fuel supply
Each pump fails differently. Lift pumps, filters and contamination get checked first.
Injectors
A miss, smoke or a rough idle. We find the cylinder first.
Holset turbos
Fixed-geometry on the 5.9, variable-geometry on the 6.7. Boost leaks and stuck vanes get ruled out first. See diesel turbo repair.
EGR, DPF and DEF
Fixed to work as built, with the upstream cause found. We do not do delete work.
Transmissions
The 47RH, 47RE and 48RE four-speed automatics, the 68RFE, the Aisin on high-output 3500s and the ZF eight-speed. Slips and heat start at diesel transmission repair.
Death wobble and front ends
4x4 Rams run a solid front axle that shakes hard when track bars or ball joints wear. See truck suspension repair.
Where Colorado driving finds the weak spots on a Cummins
A lot of the Rams we work on pull fifth wheels, campers or equipment. Long Front Range climbs hold heat for miles, and winter mornings test the starting system.
- A Cummins uses an intake grid heater, not glow plugs; a weak heater or relay means a slow, smoky cold start
- At altitude the turbo has to spin faster to make the same boost, so a small boost leak costs more power here than it would at sea level
- If the temperature gauge climbs on a long grade, ease off or pull over and let it idle; if it keeps rising, shut it off and look into truck overheating repair
- DEF freezes near 12 F, so 2013 and newer trucks need working DEF heaters
From the first call to the keys back in your hand
Four stages, any generation.
Call the shop
A person answers. Give us the year and the symptom.
Drop it off
Diagnosis typically takes 24 to 72 hours, depending on workload.
Test, then look around
Factory scan tools, hands-on testing, then the rest of the truck.
Your call
You get a list of what is urgent and what can wait, plus any jobs that cost less done together because they share labor. No work starts until you say yes.
| What moves the cost | How it plays out on a Cummins |
|---|---|
| Which pump and which era | A P7100 and a CP4 are different jobs. |
| What killed the part | A VP44 that failed because of a weak lift pump will fail again unless the lift pump is replaced with it. We quote both, so you pay for the job once. |
You hear what we found and what it costs before any work starts. A small oil leak can wait. A weak lift pump on a VP44 truck should not.
Tell us what your Cummins is doing
Send the year, the engine and what you are seeing, and we'll get back to you as quickly as we can.
- Year, make and engine
- What it is doing, and when it started
- Any codes or recent repairs
Rather talk it through? Call (303) 808-1563
What Cummins owners ask before they call
The engine pages go deeper.
Yes. Our Cummins repair work covers the 1994 12-valve through current 6.7 trucks, with the same testing for an old Dodge as a new Ram.
It might be, but check the lift pump first. A weak lift pump causes the same stall and often takes the VP44 out with it, so we test supply before we quote a pump.
It handles water and bad fuel worse than the CP3 it replaced. When one fails, it can send metal into the rails and injectors, so a pump job can grow into a fuel system job. Keep up with fuel filters, empty the water separator when the water-in-fuel light comes on, and call at the first hard start or fuel pressure code.
It can hide the shake, but it does not fix the loose part causing it. We check the track bar, ball joints, tie rods and alignment.
We do not do delete work. On a 6.7, emissions repair means finding why the EGR, DPF or DEF system failed and fixing that cause so the system works as built. The cause might be a sticking EGR valve or a DEF heater that quit in the cold.
12-valve or late‑model 6.7, tell us what it is doing.
Call with the model year and what the truck is doing, or use Request Service to send the details. Or drop us a line right here from the website and we'll get back to you as quickly as we can.