Cummins ISX Problems: Fixes for Turbo, Regen Issues, & More

Many Cummins ISX engine problems are related to the emissions control system. We’ve identified fixes for common turbo and regeneration problems — plus, a word of caution on diesel particulate filter (DPF) delete. Below, we explain what you need to know about Cummins ISX engines, their common problems, and some alternatives to consider if you are interested in a different engine brand.

What to Know Before Buying a Cummins ISX

Cummins is known for building heavy-duty diesel engines for everything from pickup trucks and tractor-trailers to farm equipment and heavy machinery. If you’re thinking of buying a vehicle with a Cummins ISX engine (or if you already have one), here are few things to know:

First, Cummins recommends a major engine overhaul around the 500,000-mile mark. Heavy-duty diesel engines should have the piston liners, bearings, and piston rings replaced at 500,000 miles, and you should also service the injection system and make any other necessary improvements at this time.

These engines can be incredibly reliable if they are properly maintained. This means understanding the needs of the DPF system (explained below), doing scheduled maintenance on time, and performing other preventative measures like oil changes and replacing injectors as needed.

There’s also an online service called Cummins QuickServe, which includes a library of information on Cummins engines and equipment. If you need specific parts or service information, you can probably find it there.

Note that heavy-duty engines (including Cummins) are subject to federal regulation by the Environmental Protection Agency (EPA). Several rules to keep in mind include:

  • Diesel engines may fall under the category of heavy-duty on-road engines or non-road emissions standards, depending on their horsepower. However, some engine standards from the EPA apply to all model years of heavy-duty engines after 1970.
  • In addition to considering your engine’s horsepower, you should follow the standards that were current in the year that your engine was built. For example, engines built since 2014 with horsepower over 751 — including Cummins’ high horsepower family — are subject to Tier 4 Final non-road rules. High-horsepower engines built between 2010 and 2013 fall under Tier 4 Interim non-road rules. Meanwhile, Cummins ISX engines typically have between 300 and 650 horsepower and are subject to heavy-duty on-road regulations.
  • Manufacturers certify new engines and vehicles before selling them. As an engine owner, your compliance with EPA standards largely involves carrying out regular maintenance and avoiding engine tampering. It is illegal for you to disable any of the emission controls after purchasing a certified engine, meaning you can’t legally remove the engine’s diesel particulate filter (DPF), exhaust gas recirculation (EGR), or selective catalytic reduction (SCR) systems.

You can find more information about emissions standards, including the full rule summaries, at the EPA website.

Common Cummins ISX Engine Problems

In the past 10 years, as the government began regulating diesel emissions more strictly, Cummins ISX engines have started to have issues with emissions systems and/or mechanical components.

If your engine won’t start, there are many potential causes — there may be an issue with the control electronics, or your ignition may be disabled after the computer’s safety system detects a fault. Dirty air filters, bad fuel, and a host of other causes could be at fault if your engine turns over but doesn’t run properly, makes unusual noises, and/or is having fuel consumption issues. However, the problem may also be mechanical. Below are some preventative measures and fixes for the most common Cummins ISX mechanical issues:

Cummins ISX Turbo Problems and Solutions

Most of the problems around the ISX turbo are due to its variable-geometry design, meaning that the compressor blades in the turbo can change their angle of attack for more or less pressure — as required by the engine. With this added complexity comes an increase in potential maintenance issues.


The actuator that controls the turbo is controlled by the Engine Control Module (ECM), so it’s worth checking to see if it’s an electronic problem first. Make sure the ECM is up to date with the most current software.

Turbo Replacement

If the problems go beyond the ECM or actuator, and you need to replace the ISX turbo, it is possible to replace it with a less complicated turbo. Swapping the turbo for a new one comes with challenges, including reprogramming the computer system. You can make the replacement yourself, but if you are unsure of how to do it and you don’t want to spend a lot of time researching and gathering parts, it may make more sense to hire a professional to do the work.

The parts and installation can be expensive — a replacement turbo will typically cost about $1,200 to $2,500 or more, depending on where you purchase it, and labor costs can double the total price. However, since it’s common to go more than 300,000 miles before issues with the turbo arise, you shouldn’t have to make the change too early or often in the life of the engine.

EGR Valve Replacement

Another problem with the Cummins ISX turbo is lack of boost, which is often accompanied by high engine temperatures. This points to a problem with the EGR valve. Replacing the EGR valve, as well as cleaning the turbo hot side (or possibly replacing it), should resolve the issue. It also helps to get your engine regularly checked and maintained.

You can replace your EGR valve by yourself if you prefer to not pay a professional to do it. Advance Auto Parts even provides step-by-step instructions for replacing the valve.

Cummins ISX Regen Problems and Solutions

To properly maintain a Cummins ISX engine, the DPF needs to be cleaned regularly through a process known as a diesel regen or regeneration. This is another complicated emissions control system intended to improve air quality. A common problem in ISX engines is the DPF not regenerating. Idling issues are the leading cause of problems with the emissions control systems in these engines; often, trucks that are driven and then let to sit idle can’t regenerate properly.

While it is possible to clean the DPF yourself, you may want to have a professional do it to ensure that it is done thoroughly and in accordance with EPA standards. TA/Petro offers DPF cleaning services at locations around the country, and it typically costs around $350.

You can also prevent or solve regen problems by simply shutting off the engine when you’re not driving, or switching the truck to high idle if it is running while parked, so it runs at a temperature high enough to cut down on clogging. The engine should automatically regenerate when properly maintained, but will still need occasional manual regeneration, as the DPF gets dirty over time even with automatic regen.

Cummins ISX DPF Delete

“DPF delete” is the process of removing a vehicle’s DPF and configuring the vehicle’s system to work without it. While it is possible to remove the DPF system and other parts of the emissions control system from a vehicle, this is illegal in the U.S. due to the EPA’s emission standards, as detailed above.

Removing any pollution-control element from your engine is in violation of the EPA’s on-road and non-road engine regulations. If you tamper with your engine and then operate your vehicle in an area where it’s illegal to modify an emissions control system, you may face hefty fines or criminal penalties for violations. Make sure to review all applicable laws in your area of operation before you make a change.

Cummins ISX Engine Alternatives

Since there are several known Cummins ISX engine problems — especially with the complicated emissions control system — you may be wondering about alternatives. A few of Cummins’ top competitors are Detroit, International, and Paccar. Keep in mind, however, that these companies are bound by the same EPA requirements, so the engines may face similar issues. When buying a truck or a piece of heavy machinery, the manufacturer will provide engine options, if any are available. If a Cummins engine is your only factory option but you’d like something else, a custom engine swap is a pricey alternative. Super Street Online offers a detailed explanation about how to go about a custom engine swap.

In Summary

Some of the most common ISX engine problems are related to the emissions control system, which you cannot tamper with or remove. These systems have grown increasingly complicated as diesel emissions have become more strictly regulated, which has led to increased issues with the turbo, EGR valve, and DPF. However, with proper care and maintenance, such as replacing the EGR valve, cleaning the DPF regularly, and not leaving the engine idling, these engines should be able to last for 300,000 to 500,000 miles or more before needing serious work.