P0633 Code: Immobilizer Key not Programmed – ECM / PCM

The immobilizer key is one of the security measures that protect your vehicle from thieves. It replaces the traditional metal key that you insert into the door lock cylinders and ignition cylinder. Without the immobilizer key, you cannot lock, unlock, start, and turn off your vehicle.

If you try to start the vehicle with an ignition key that isn’t programmed into the anti-theft control module, its diagnostics will log a P0633 code and the anti-theft light will switch on.

What Does the P0633 Code Mean?

The diagnostic trouble code (DTC) P0633 indicates “Immobilizer Key not Programmed – ECM/PCM.”

The immobilizer key fob contains a transponder that emits an electronic signal and runs on a small internal battery. When the key fob comes within range of your vehicle, it sends the signal to controllers like the engine control module (ECM) or powertrain control module (PCM).

If everything is working properly, the car’s computer unlocks the doors and enables the push-to-start button. Conversely, moving the immobilizer key out of reach of the vehicle does the opposite—the doors lock and the push-to-start button is deactivated.

Each immobilizer key has a transponder signal that only it possesses. The signal for your car’s stock key is programmed into the relevant controllers—the ECM/PCM, the anti-theft control module, and the body control module (BCM).

If the immobilizer key is replaced, the new key’s transponder signal must be programmed into the controllers. Likewise, a new ECM/PCM will need the old key fob’s signal entered into its memory.

The PCM regularly checks the fob signal from the immobilizer key and compares it with the signals programmed into the anti-theft control module. If the controller detects a transponder signal that it does not recognize, it will set the general code P0633.

Note: The definition of DTC P0633 can differ according to the vehicle manufacturer. Check the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0633 Code?

• Bad anti-theft control module
• Ignition key isn’t programmed to the vehicle
• Problem with the wiring like corrosion and shorted circuit

What are the Common Symptoms of the P0633 Code?

• Anti-theft light is switched on
• Engine won’t start

How to Diagnose the P0633 Code

The P0633 code is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles built from 1996 or later. Despite being a generic code, the specific steps of the repair process can vary according to many factors.

If you’re not confident about conducting diagnostic tests on your vehicle, it’s a good idea to bring it to a professional mechanic. Otherwise, you can go ahead and diagnose the issue yourself.

How to Fix the P0633 Code

Attempting to fix a P0633 code can become a frustrating task if you don’t have the right tools and know-how to test the anti-theft module. In most cases, it’s best to leave the job to professionals.
For DIYers with advanced technical knowledge and hands-on experience who prefer to test and replace their vehicle’s anti-theft control module on their own, it will be helpful to rely on the appropriate repair manual or refer to an online repair database.