5.9 Cummins Check Engine Light

Is the Check Engine Light (CEL) on in your 5.9L Cummins truck? That’s the engine’s way of telling you something is wrong. It could be anything from injector or turbo issues to fuel systems or emissions problems. Ignoring it can lead to more significant problems like poor performance or costly repairs. Addressing the issue early helps keep your truck running smoothly, improves fuel efficiency and prevents long-term damage. 

Why Is the Check Engine Light on in Your 5.9L Cummins?

Many circumstances could lead to your 5.9L Cummins check engine light coming on. 

Injector Issues

If your truck is misfiring, experiencing poor acceleration or getting reduced engine power, it might have an injector issue. Debris in the injector’s spool valve can cause restricted fuel flow and poor injector performance. To fix injector issues, clean or replace the affected injectors and use a fuel additive to clean the system. 

• Low fuel pressure, clogged fuel filters, or a failing lift pump can cause fuel delivery issues.
• A P0088 (Fuel Rail/System Pressure Too High) or P0087 (Fuel Rail/System Pressure Too Low) code may appear.

Turbocharger Problems

When your engine light is on and your truck exhibits a loss of power, decreased acceleration and more exhaust smoke, the turbocharger could be the problem. There are two possible causes: 

• Varnish on the turbo bearings: Stiction (the sticky friction) on turbo bearings lead to improper turbo operation or failure. Try Stiction Eliminator to clean the turbo bearings or replace turbocharger.
• Oil contaminates the turbo system: When the turbo system becomes contaminated, it causes performance issues. To address the issue, inspect and replace any damaged components.
• A boost leak or a faulty boost pressure sensor: can also trigger warning codes, inspect for leaks. 

Exhaust Gas Recirculation (EGR) Issues

If your truck has EGR issues, it might idle rough, exhibit poor acceleration and release excess smoke due to:

• Blocked or malfunctioning EGR valve: Problems with the EGR valve affect the air-to-fuel ratio. Clean or replace the EGR valve to address the issue.
• Carbon buildup in the EGR system: Carbon buildup restricts the EGR system. Clean the EGR system to remove the buildup.

Fuel Delivery Problems

The check engine light could indicate fuel delivery problems, hard starting, rough idling and engine hesitation. Here are two possible causes:

• Faulty fuel pump or pressure regulator: If your fuel pump or pressure regulator is malfunctioning, you’ll need to inspect and replace it.  
• Clogged fuel filter: If you use low-quality fuel or have a clogged fuel filter, check for visible debris or damage and use a fuel pressure gauge to measure the pressure. Low pressure could indicate a clogged filter, and replacing the filter would fix the issue. 

Faulty Sensors

Faulty sensors are another issue that could turn your check engine light on. If you notice erratic engine behavior or poor fuel economy and acceleration, you might have a faulty mass airflow (MAF) sensor, oxygen sensor or crankshaft position sensor. Test to determine which ones are faulty and replace them. 

There are a few ways to diagnose your Cummins 5.9L check engine light. 

Scan for Diagnostic Trouble Codes (DTCs)

Use an OBD-II scanner, a diagnostic tool that fits into your truck’s OBD port and reports your vehicle’s diagnostic trouble codes. Some Dodge Ram trucks allow you to check codes without a scanner by cycling the key ON-OFF-ON-OFF-ON (without starting). The codes will appear on the odometer. If the issue is related to injectors or turbo performance, look for codes indicating poor fuel atomization or turbo performance. Also, check for codes related to sensor issues. Here are a few notable codes:

• Injector circuit codes: P0200-P0204
• Turbo over boost: P0234
• Mass airflow sensor: P0101
• Transmission Control System: P0700

Visual and Physical Inspection

Inspect your 5.9L Cummins fuel injectors, turbocharger and sensors for visible damage or wear, such as leaks and signs of carbon buildup. Also, check for debris around the turbo and injectors.

• Check for loose or damaged hoses (boost leaks, vacuum leaks).
• Look at fuel lines and filters for signs of blockage or leaks.
• Inspect the turbocharger for excess shaft play or excessive soot buildup.

Test Sensors and Components

Perform tests on the MAF, crankshaft, and other sensors and components, such as injectors and turbo, to check for low or erratic performance. Use a multimeter or other diagnostic tools to check the sensor readings and determine if the sensors need cleaning or replacement. 

Use our third-party tested fuel and oil additives to significantly minimize the risk of check engine light issues by improving fuel system performance and reducing harmful deposits.  

Hot Shot’s Secret Diesel Extreme

Hot Shot’s Secret Diesel Extreme is a powerful fuel treatment designed to clean injectors and restore overall fuel system efficiency. It removes stubborn carbon buildup, significantly improving injector performance. Add it to the fuel tank to clean your injectors and restore optimal fuel system functionality. Regular use helps prevent future injector and fuel system issues, ensuring long-term reliability and performance. 

Hot Shot’s Secret Everyday Diesel Treatment (EDT)

Hot Shot’s Secret EDT is a comprehensive solution for maintaining your fuel system’s health. It cleans and lubricates the entire system, including injectors, ensuring smooth and efficient operation. EDT keeps your diesel engine running at its best by improving fuel economy and preventing issues like injector clogging. Add it to your fuel tank at every fill-up to maintain peak fuel system performance and long-term reliability.