How to Fix the P0633 DTC Code on Cummins (Expert Insights)

Diagnostic Trouble Code (DTC) is pretty typical for any modern vehicle. You never know when you have to deal with the codes. In addition, it’s also important to fix the code as immediately as you can to get rid of major problems related to your vehicle. 

The P0633 code on Cummins is an OBD2 code that occurs if the engine control module (ECM) or power control module (PCM) finds an unrecognized immobilizer key. In its simplest form, the code means Immobilizer Key Not Programmed – ECM / PCM.

There are many reasons behind this trouble code. Nonetheless, you should resolve the code as soon as possible for the betterment of your truck. That’s why we will give you more in-depth information about the code and how to fix it. 

How to Fix the P0633 DTC Code on Cummins

What Does Code P0633 Mean On Duramax?

When the engine control module (ECM) or power control module (PCM) cannot identify the immobilizer key, the diagnostic issue code P0633 appears. This trouble code applies to vehicles made after 1996. 

The immobilizer is one of the critical devices that ensure the safety of cars. In addition, the immobilizer key disallows the engine from being started unless the correct key is present.

Therefore, it’s a must for the car’s controller- PCM or ECM to detect the transponder signals of the immobilizer key fob.  But what if this doesn’t happen or the ECM or immobilizer key is not programmed after being replaced?

Then, the code P0633 will be stored, and the malfunction indicator lamp (MIL) will be illuminated.

Now, let’s break down the code below.

  • P= Powertrain
  • 0= Standard OBD2
  • 6= Onboard Computer
  • 33= Specific Fault Index (Here, it indicates Immobilizer Key not Programmed – ECM / PCM)

How Serious Is Code P0633 On Cummins?

The P0633 code on Cummins is stored; you won’t be able to start your truck. So the code is a more serious threat to you and your vehicle. Therefore, it is essential to program the immobilizer key and the PCM or ECM accordingly.

When the car’s controller detects an immobilizer key that is not recognized, the car computer won’t allow the vehicle to be unlocked, enabling the push-to-start button. So, at the end of the day, you won’t be able to start your car.

The car’s engine is automatically locked down, and unless you fix the code, it will be impossible for you to operate your car. 

But, here’s a catch! Sometimes, the onboard computer in your vehicle can misread the code. So, if this happens, you can still drive your vehicle after clearing the code. 

What Causes P0633 Code On Cummins?

Many factors can cause the P0633 code on Cummins. Among them, the primary cause is when the PCM/ECM identifies an unrecognized immobilizer key. 

In addition, let’s look at some of the causes of the P0633 code.

  • Faulty anti-theft control module.
  • A defective immobilizer key battery.
  • Immobilizer key malfunction.
  • Problems with corrosion and shorted-circuit.
  • PCM or ECM is replaced without being programmed.
  • PCM or ECM malfunction. 
  • Bad ignition cylinder.
  • Bad anti-theft control system. 

What Are the Symptoms of the P0633 Code on Cummins?

You will notice a few symptoms that indicate the P0633 code on Cummins. However, the most common symptom is activating the vehicle’s security system.

In addition, the other symptoms are;

  • The truck refuses to start.
  • The lock/unlocked function is disabled.
  • Other diagnostic codes can be stored.
  • The engine light is on.

How To Fix Code P0633 On Cummins?

Fixing this type of troubleshooting code is not like walking through the part. Instead, you need to have enough expertise regarding the issue. 

In addition, you should also know your truck’s component functions to fix the code comprehensively.

Nonetheless, you must diagnose the code p6033 with an OBD 2 scanner. Once done with it, you can follow the steps below to fix the code.

Step 1: Verify the Code with a Code Reader Scanner and Attempt to Clear the Code

Here, you need to verify the code with the help of the OBD2 scanner. Once you have verified the problem, you should try to clear the code to make sure whether the code returns.

Step 2: Determine Electrical Wiring Problem

You need to be sure there are no electrical wiring problems. The OBD-II scanner can help you by letting you know whether there is any damaged or corroded wire or connection. 

Step 3: Replace or Repair the Electrical Wire

If you find any corroded wire, you should repair it. In addition, replacing the corroded or damaged wire is better if the repair won’t fix the problem. If there is no issue with the electrical wire, follow the next steps.

Step 4: Reprogrammed the Immobilizer Key 

You need to reprogram the immobilizer key if the  PCM/ECM does not recognize any immobilizer keys. Most of the time, reprogramming an immobilizer key can solve the P0633 code. 

Step 5: Replace Immobilizer Key Battery

However, if you can fix the P0633 code by reprogramming the immobilizer key, the lower or weaker immobilizer battery can cause the code on your truck. So, it’s essential to change the battery.

Step 6: Replace and Reprogram the PCM or ECM

An unintentional immobilizer key signal displayed by the scanner means the PCM/ECM was replaced without being programmed. So, you have to replace it now. 

Reprogramming the PCM or ECM can be tricky. As a result, it is better to go for a professional. Besides, make sure you replace the PCM or ECM before reprogramming it. 

Sometimes, the controller may malfunction, and you will need to replace it in this case.

Step 7: Repair Defective Ignition Cylinder

A defective ignition cylinder can be the cause of the code P0633. So, it is much better to repair the ignition cylinder to fix the code if the above steps don’t work. 

How Much Does It Cost To Fix P0633 Cummins Code?

The cost of fixing Cummins P0633 depends on a few factors. First, the cost often varies based on the problem types that can cause the code and locations.

However, if the immobilizer key is needed to fix it, it can cost around $300, including labor costs. Therefore, the cost of programming the immobilizer key and PCM/ECM depends on the service provider. 

On the other hand, if you need to replace the PCM/ECM, it can cost you a lot of money. On average, the cost will be about $800-$1500. 

In addition, the only cost to diagnose may be around $75-$150 per hour. Besides, to repair the ignition cylinder, you have to spend about $70-$200. 

Can You Drive Your Cummins With Code P0633?

Unfortunately, you can’t drive your car with the code P0633. This is because if the PCM/ECM of your car detects an immobilizer key that is not recognized, it won’t allow the engine to start. 

But, there is a point when you can drive your truck. If the computer on your vehicle can’t read the code correctly, you can still drive your truck. However, this doesn’t happen all the time. 

If you notice the code while driving, you should stop your vehicle and repair it immediately. 


We believe you have found this article helpful and will find it much easier once you notice the P0633 troubleshooting code on your truck. Nonetheless, it’s crucial to determine the actual cause before taking corrective steps.

Additionally, it is also important to diagnose the code properly with the OBD 2 scanner. However, ensure you carefully review all the procedures mentioned in this article to fix the Cummins P0633 code.

You should undoubtedly go with a professional if you don’t have the expertise and tools to fix the code. However, the most important job is to fix the problem as early as possible.

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