5.9L Cummins Issues: Troubleshooting & Solutions (9 Common Problems + Fixes)

Last updated: January 2026

9 common problems with the Dodge Ram 5.9L Cummins turbo diesel and how to fix them

Even the most reliable engines have their own particular issues and the 5.9L Cummins is no exception. Although Cummins engines have a reputation for being reliable, there are certain problems that you may encounter.

Key Takeaways

  • Fuel supply is everything: a weak lift pump can shorten VP44 injection pump life and cause hard-start/no-start.
  • Cracked manifolds and boost leaks can create power loss, exhaust smell, and poor idle—fix early to prevent collateral damage.
  • Turbo oil seal wear can push oil into the intake/exhaust and create runaway-risk symptoms—inspect promptly.
  • APPS and ECM issues can mimic drivability/fueling problems—diagnose with a scan tool before replacing parts.

Quick Answer

The most common 5.9L Cummins issues involve fuel delivery (lift pump/VP44/injectors), exhaust manifold cracking, sensor/ECM-related drivability problems, and turbo wear. Use symptoms (hard starts, low power, smoke, exhaust smell, poor idle) + a scan tool to confirm the cause before replacing components.

Jump To a Problem

Here are 9 common problems with Dodge Ram Cummins turbo diesel and how to fix them.

VP44 injection pump for Dodge 5.9 Cummins (1998.5–2002)

5.9L Cummins Fuel Pump, Injection Pump, and Injector Failures

When your fuel pump starts to fail, it may not be immediately apparent, as the injection pump will still be drawing fuel. The injection pump can’t do the job on its own indefinitely, however, and will wear down, resulting in a loss of power. If your engine is difficult to start, or not starting at all, it may be the injection pump. Diagnosing this will require a scan tool.

  • Common symptoms: hard start/no start, low power, surging, stalling, trouble codes, erratic fueling.
  • Common fix: verify lift pump pressure/volume, then diagnose VP44/injector issues with a scan tool.
  • Prevention tip: keep fuel filters fresh and address low fuel pressure early to protect the injection pump.

Whether you need a fuel pump or injection pump, BD Diesel has you covered with the highest quality replacement parts.

5.9L/6.7L Cummins exhaust manifold upgrade

5.9L Cummins Cracked Exhaust Manifolds

A cracked exhaust manifold is something that needs to be attended to quickly as it can cause damage to other parts in your engine bay. Hot exhaust gases may melt wires or even cause combustible parts to ignite. Engine misfires, exhaust smell, poor idling, and loss of power are some of the signs of a cracked manifold.

  • Common symptoms: ticking/“chuffing” sound cold start, exhaust smell in bay, soot marks near the crack, lower boost/power.
  • Common fix: repair (braze/weld) if minor and feasible, otherwise replace with an improved manifold.

If the crack is small, visiting a garage that specializes in exhaust systems may save it if they are able to braze or weld it. If not, you will need to replace it.

5.9L Cummins ISB Dead Accelerator Pedal

Pressing down on your accelerator and finding it unresponsive is disconcerting and can be a major cause for concern. It is also not uncommon in Ram Cummins models. The cause may be due to improper calibration, or perhaps a malfunction in the accelerator pedal position sensor (APPS).

  • Common symptoms: throttle dead spot, inconsistent pedal response, limp mode, intermittent power.
  • Common fix: scan for codes, verify APPS signal and wiring, then calibrate/replace as needed.

An experienced service technician familiar with this problem can likely fix it, but to avoid dealing with the issue in the first place, some things to try include frequent replacement of your fuel filters, repairing loose plugs and wiring, and updating your turbo’s software.

5.9L Cummins ECM Failure

The engine control module is responsible for hundreds of operations from fuel delivery to engine timing and much more. Several factors can lead to failure, but the most common is component failure. Simply put, the components have a lifespan and once it’s been reached, they can fail.

  • Common symptoms: random no-start, communication errors, intermittent sensor readings, unexplained limp mode.
  • Common fix: confirm power/ground integrity first; then consider repair/rebuild or replacement if the module is faulty.

The ECM can be repaired if the faulty parts can be replaced. It is also possible that the failure is due to software bugs, so while you may end up replacing it, you may want to check first if repair is an option.

5.9L Cummins Clogged DPF (Diesel Particulate Filter) — Clarification

Important note: Most factory 5.9L Cummins applications (1998.5–2007) do not use a factory DPF. If you’re experiencing “restriction-like” symptoms on a 5.9L, the issue is more commonly related to exhaust restriction (damaged muffler/catalyst if equipped), fueling, or turbo/boost leaks.

If your truck has been emissions-upgraded or swapped, a particulate filter can become clogged. In that case, you may try cleaning methods or approved additives, but persistent restriction usually requires proper diagnosis and service/replacement of the restricted component.

5.9L Cummins Sticking/ Stuck Variable Geometry Turbocharger (VGT) — Note

The variable geometry turbocharger is an effective means of achieving power in different engine conditions, but it is unfortunately also prone to both mechanical and electronic failures. The real problem with the VGT is that the moving parts in the turbo housing become coated with oil, soot, and ash, impeding the movement of the VGT and causing a decrease in performance.

Note: Many 5.9L Cummins trucks run fixed-geometry turbos from the factory. However, the same “sticking mechanism” concept can apply to wastegate issues, actuator problems, or aftermarket VGT conversions. A sticking or stuck mechanism will normally require disassembly and manual cleaning (or repair) to restore functionality.

HE351CW turbo upgrade option for 5.9L Cummins (2003–2007)

5.9L Cummins Turbocharger Failures

Perhaps the most common failure on the 5.9L Cummins turbo is the oil seals. Worn seals in the centre hub rotating assembly can allow lubricating oil into the intake and exhaust. This can be problematic as the intercooler can be clogged by oil in the intake. The oil can also cause an increase in engine RPM beyond the throttle input. Oil in the exhaust, meanwhile, can damage the oxygen sensors.

  • Common symptoms: oil in intercooler piping, excessive smoke, loss of boost, unusual noises, rising oil consumption.
  • Safety note: if engine RPM rises unexpectedly, shut down safely—this can indicate oil ingestion.
  • Common fix: inspect shaft play/seals; rebuild or replace turbo if wear is confirmed.

Removing the turbo to take it apart and clean it may help, but is not a permanent solution. Most often it will need to be replaced.

5.9L Cummins Head Gasket Failures

This is not the most common issue with the 5.9L as it is under less pressure than the 6.7L. Some signs of failure include white smoke from the tailpipe, coolant loss with no visible leak, engine overheating, and bubbling in the radiator and coolant reservoir.

  • Common symptoms: overheating, pressure in cooling system, coolant loss, white smoke, bubbles in reservoir.
  • Common fix: confirm with pressure test / combustion gas test; repair properly if gasket failure is verified.

5.9L Cummins Fuel Dilution

Although fuel dilution is normal and expected to a limited degree, excessive dilution can contaminate the engine oil, reducing oil viscosity. This in turn leads to greater engine wear. You could try a fuel-system cleaner, but in some cases the culprit might be a piece of debris lodged in an injector tip that prevents it from closing. While a fuel-cleaner might help, you may also require a trip to your mechanic.

  • Common symptoms: rising oil level, strong diesel smell in oil, thinner oil, increased wear/noise.
  • Common fix: identify leaking injector or fueling fault; change oil after repairing the root cause.

Recommended Parts & Next Steps

While none of these issues are guaranteed to occur, some of them are common enough that you should be aware of them and watch for warning signs. If and when you encounter one of them and require a replacement part, BD Diesel has you covered with high-quality parts that meet and often exceed the original. For more information, contact us today!

FAQ: 5.9L Cummins Problems & Troubleshooting

What years are considered the “5.9 Cummins” in Dodge Ram trucks?

In most cases, Dodge Ram 2500/3500 trucks used the 5.9L Cummins from 1998.5 through 2007 (with different fuel system/turbo configurations by year).

What are the most common VP44 injection pump failure symptoms?

Common signs include hard starting, stalling, low power, surging, and trouble codes—often tied to weak lift pump pressure over time.

Can a weak lift pump really damage the VP44?

Low fuel supply can force the injection pump to work harder and run hotter. Verifying proper fuel pressure/volume is a smart first step before replacing major parts.

How do I know if my exhaust manifold is cracked?

Look for ticking/chuffing sounds (especially cold start), exhaust smell in the engine bay, soot streaks around the manifold, and reduced boost/power.

What causes a “dead pedal” on a 5.9 Cummins?

Often it’s APPS calibration/sensor signal issues, wiring/connectors, or an ECM-related drivability fault. Scan for codes and verify the signal before replacing parts.

Does a factory 5.9 Cummins have a DPF?

Most factory 5.9 applications do not. If you have restriction-like symptoms, consider exhaust restriction (if equipped), fueling, or turbo/boost leaks.

What are signs of head gasket trouble on a 5.9 Cummins?

Coolant loss with no visible leak, overheating, bubbling in the reservoir, and white smoke can indicate a problem—confirm with proper testing.

What should I do if I suspect turbo oil seal failure?

Inspect intake piping/intercooler for oil, check shaft play, and address it quickly—oil ingestion can create unsafe engine behavior.