6 common Bad ECM Symptoms On Duramax (Easy Solutions)

Imagine you are going on a long road trip on a clear, sunny day. Your Duramax truck is equipped with all the camping gear. And all of a sudden, you see the check engine light coming on the dashboard. You lose acceleration and the truck stops after a while.

Even after trying to start the engine, it misfires and doesn’t start. All these are symptoms of a bad ECM on your Duramax vehicle. I am going to share the Duramax Bad ECM Symptoms from my experience of working as an auto technician for a few decades.

Along with that, I will also tell you how to diagnose and fix those problems. Let’s get started with what an ECM is.

6 common Bad ECM Symptoms On Duramax (Easy Solutions)

What Is an ECM and How Does It Work?

An ECM or Engine Control Module is an onboard computer system that monitors and controls your vehicle’s performance. This component is also known as an ECU or Engine Control Unit.

It has four main responsibilities. They are to control the ratio in the air-fuel mixture, idle speed, variable valve timing, and ignition timing. The ECM uses different sensors to collect data from various vehicle parts and processes them to control the performance.

By determining the right air-fuel ratio or the exact ignition timing, an ECM ensures the optimal performance of a Duramax engine.

Read also >> Duramax EGR Valve Symptoms: (Causes & How To Fix Guide)

6 most Common Bad ECM Symptoms on Duramax

You can easily identify a bad ECM if you know these common symptoms and the device is in the self-diagnostic cycle. Check them out.

1. Check If the Engine Light Comes On

As modern vehicles are equipped with state-of-the-art computer systems, you will get notifications for even the slightest fault. An illuminated Check Engine light will show up on the dashboard if anything goes wrong with the ECM.

Though the Check Engine light can come up for many reasons, the most common cause is the fault in the ECM, sensors, or wiring.

2. Engine Stalling

While running, your Duramax engine might suddenly stall if the ECM is bad. This can also happen due to a faulty or loose connection where you will see the engine stalling at an uncertain pattern.

3. Stuttering or Misfiring

If your vehicle engine stutters or misfires while starting, it is most probably caused by a bad ECM. A too-rich or lean mixture of air and fuel can cause stuttering or misfiring. This can occur when the ECM isn’t able to regulate the ratio of the air-fuel mixture.

4. The engine Won’t Start

As the ECM regulates everything in modern vehicles, a serious problem in the ECM might not let the vehicle start. You might face hiccups while starting the vehicle, or the vehicle won’t start up at all in the worst cases.

5. Decreased Engine Performance

If some of the sensors of Duramax have no communication with ECM, it might affect the engine’s overall performance. As a result, you might notice power loss or poor acceleration.

6. Decreased Fuel Efficiency

Another important symptom of a bad ECM is poor fuel efficiency. It means the ECM cannot regulate the optimum air-fuel mixture in the engine.

How Do You Test Duramax ECM?

If you want to inspect the ECM of your vehicle at home, here are the ways I mostly use to test Duramax ECM. Give them a try to find out whether your ECM is working fine.

Using an OBD2 Scanner

OBD or On Board Diagnostic scanners are commonly used to precisely identify the problem in your vehicle’s ECM. FIXD is a very popular OBD2 scanner that you can connect to your vehicle using the OBD port or the C2 connector. The device will test the ECM to find out the possible faults and show you how to solve them.

In some cases, the scanner might suggest you avoid driving. For example, if the scanner shows the P0700 code, it means the fault is in the TCM or Transmission Control Module.

If the code shown on the scanner is P0602, it means there are problems in the Duramax ECM programming. Other codes have their meaning that will indicate the exact problem.

Visual Inspection

In this case, you need to check the ECM for any faulty parts or connections physically. Check whether the pins of the connector are intact or not. Also, check whether all the electrical connections are correctly made. You should also sniff the ECM for any burning smells.

Swap and Elimination

You can check different inputs and outputs to test the ECM. The last resort is to replace the ECM, but it isn’t possible with OBD2 cars. You can only replace the ECM in OBD1 cars that were made before 1996.

What Causes Bad ECM on Duramax?

Your Duramax ECM can go bad for various reasons. The most common reason can be a fault in wiring or a broken or disconnected sensor. If the Duramax ECM relay location is too far, wiring problems can occur midway. As a result, the ECM might not get enough data from the sensors.

If the wiring or ECM pins get damaged, it may also cause the ECM to go bad. A bad battery can also be the reason behind a bad ECM on Duramax.

How to Fix Duramax ECM Failure?

Fixing a bad ECM on Duramax will depend on the type of problem. If the problem is caused by an error in the programming of the ECM, you can fix the problem with a Duramax ECM reset. Before that, check whether you should do it yourself here.

If you have any broken sensors or damaged wiring, you might need to replace them to fix the problem. And if the ECM itself is faulty, you need to replace the part with a matching one.

people also ask (FAQ)

Here are the answers to some questions people frequently asked me when I worked as a technician.

Why do Duramax ECMs crash?

The ECM on your Duramax can crash if you don’t unplug all fuses before flashing. If the battery voltage drops too much during a flash, the ECM might also crash.

Can an ECM be repaired?

It depends on the fault level of the ECM. If there is a fault in the programming, it can be reset. But if the mainboard or pins are broken, you might need to replace them.

Can I delete the ECM to start the engine?

Unfortunately, no. The ECM controls almost every function of the engine. So, if you remove it, you won’t be able to start the vehicle.

Can I replace the ECM on Duramax myself at home?

If you have the proper knowledge and tools to replace the device, you can try it yourself at home. But if not, it is better to consult an experienced technician.

2015 GM Truck 2500 HD 6.6 LML No Crank No Communication With ECM Diagnosis >> Check out the video below:

Final Words

As new technologies are taking over the auto industry, the latest computer systems are now controlling almost every engine function of a modern vehicle. These systems can detect issues on their own and show you warning signs to solve those issues as soon as possible.

Besides, you might notice some symptoms that will tell the ECM on your Duramax has gone bad. You should also run regular inspections for any fault in the ECM of your vehicle to ensure the vehicle performs well.

I put all my experience to let you know the common symptoms of bad ECM, the common causes behind them, and the easiest fixes to resolve issues. Next time you have any of these issues, try these ways out.

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Who Worked on This post?



Anderson is an experienced auto mechanic with over 10 years in the industry. He is skilled in diagnosing and repairing a wide range of vehicles, from sedans to trucks and SUV

Syed Ahmed


Syed Ahmed has been working as an auto mechanic editor for the past five years. He has a background in mechanical engineering and a love for all things automotive

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