cummins isx will turn over but will not start


The Troubleshooting Guide for Cummins ISX That Will Not Start

If you are an owner or operator of a truck with Cummins ISX engine, you might have encountered the frustrating issue of it not starting. There could be several reasons behind it, ranging from minor problems to major malfunctions. In this article, we will guide you through the troubleshooting process to help you get to the root of the problem.

Step 1: Check the Batteries

The first and foremost thing to check when your Cummins ISX engine won’t start is the batteries. Make sure they are not worn out, corroded or dead. Check the connections for any loose or damaged terminals. Use a multimeter to check the voltage across the batteries. If the readings are below 12 volts, then it’s time to replace the batteries.

Step 2: Fuel System

The fuel system of your Cummins ISX engine is another area to inspect when it won’t start. Check if there is fuel in the tanks and that it is reaching the engine. Make sure the fuel filter is clean and free of debris. Sometimes, air bubbles can form in the fuel lines, which can cause the engine to stall. Purge the fuel lines to remove any air present in them.

Step 3: Faulty Starter Motor or Alternator

The starter motor and alternator are the two main components of your vehicle’s electrical system. A faulty starter motor or alternator can cause your Cummins ISX engine to not start. Check the starter motor for any sign of damage or wear and tear. Use a voltmeter to check the output of the alternator. If the output is below the acceptable range, then it’s time to replace the faulty component.

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Step 4: Check the ECM

The ECM (Engine Control Module) is responsible for controlling the engine’s various components. A malfunctioning ECM can prevent your Cummins ISX engine from starting. Check for any error codes or warning messages on the dashboard display. Use a diagnostic tool to scan the ECM for any faults or errors. If you find any, then address them immediately.

Step 5: Spark Plugs, Injectors, and Timing

If everything else checks out fine, then it’s time to inspect the spark plugs, injectors, and timing. Check the spark plugs for any damage or corrosion. Inspect the injectors for any clogs or leaks. Use a timing light to check if the timing is accurate. If any of these components are faulty, then it’s time to replace them.


These are the five main areas to inspect when your Cummins ISX engine won’t start. Regular maintenance and timely inspections can prevent such issues from arising. If you encounter any major malfunctions or issues, then seek professional help immediately. We hope this troubleshooting guide helps you diagnose and address any issues with your Cummins ISX engine.