Error Code P0633 is defined as Immobilizer Key Not Programmed – ECM/PCM. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly vehicles made since 1996 up to present. This includes vehicles from, but not limited to, Cadillac, Chevrolet, Chrysler, Dodge, GMC, and Jeep. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
Then Error Code P0633 is stored, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined an immobilizer key that it doesn’t recognize.
The job of the immobilizer key is to key the vehicle safe from theft and eliminate the need to use an actual metal key into the door lock cylinders, or ignition cylinder. A transponder powered by a small battery is equipped into the immobilizer key fob. When the key fob is inside a certain distance from the vehicle, a transponder emits a signal to the PCM and other controllers. Usually, when a transponder signal is received, the doors are unlocked, and the vehicle’s push-start button is activated. When the immobilizer key is moved away from the doors, the door locks automatically, and the push-to-start button will be deactivated.
Every immobilizer key emits a unique signal. For onboard controllers to recognize this signal, they must be programmed appropriately. The PCM and security control module are both responsible for engine starting, while the BCM (body control module) is responsible for the functions of door and trunk lock/unlock.
Thus, this being said, when PCM or immobilizer is replaced, it must be programmed.
If the PCM is unable to recognize the immobilizer key, and the vehicle entry or start-up is attempted, Error Code P0633 will be triggered, simultaneously activating the Check Engine light. The immobilizer key transponder signature is compared between the PCM and other controllers, each time the security system is activated, and self-test function is energized.
- No start condition
- Disabled lock/unlock function
- Vehicle security system may be activated
Other related diagnostic code may be present.
- Recently replaced PCM was not programmed to match the vehicle and its immobilizer key
- Faulty ignition cylinder
- Faulty PCM
- Open or short in connectors or wirings
Dead battery discharged for an extended period of time can cause the PCM to lose programming, which means it needs reprogramming.
How to Check
Because of the delicate nature of certain parameters that must be programmed to the PCM (mileage, VIN), reprogramming equipment access is limited only to qualified personnel. Thus, without the tool to reprogram the troubled controller, successful repair for this problem is highly unlikely.
Though this code is usually caused by controller failure, or some controller programming error, battery problem with the transponder or immobilizer key can also cause this issue.
For a more accurate diagnosis, you need a diagnostic scanner and reliable vehicle information source for this code. Find a TSB that matches with the vehicle make and model, symptoms of the problem, and code stored, as this will help you to point to the right direction.
By connecting the diagnostic scanner to the vehicle diagnostic port, you can see whether the PCM (and other controllers) are recognizing the immobilizer key. This information is typically shown as a yes or no, without a specific transponder description. If the PCM is not recognizing the immobilizer key, then you can suspect the battery is dead in the key fob, or the wrong immobilizer key is being used.
If an inadvertent immobilizer key yes signal is shown on the scanner display, you can suspect that the PCM may have been replaced without programming it to match with the vehicle. If this is not the case, then you can suspect failed PCM problem or programming error.
In some cases where reprogrammed, aftermarket, replacement controllers and immobilizer keys may be purchased, it is important to provide the parts vendor with the mileage and VIN of the vehicle, as well as its secondary (factory programmed) immobilizer key.
Replacement of any component of VSS (vehicle security system) or controller usually requires reprogramming.
How to Fix
- Repair or replacement of electrical wiring problems, connectors, and fuses
- Replacement and reprogramming of PCM or another control module
- Assess and repair of defective cylinders in the ignition
Since this code keeps the vehicle from starting, it’s a serious condition.
Unfortunately, though, diagnosis and resetting of the code will not always fix the problem, as it requires reprogramming. Vehicle ID, mileage, and anti-theft settings are all required to reset before the vehicle can be operated.