Technical Description of OBD-II Trouble Code
ECM/PCM – Immobilizer Key Not Programmed
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Dodge, Ram, Chrysler, Jeep, Chevy, GMC, Cadillac, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
When code P0633 is stored, it indicates that the engine control module (ECM) or powertrain control module (PCM) has detected an unrecognized immobilizer key.
The immobilizer key is designed to prevent vehicle theft and eliminate the need for a physical metal key in the door lock cylinders or ignition cylinder. It contains a transponder that emits a signal to the ECM/PCM and other controllers when it is within a certain distance of the vehicle. This signal unlocks the doors and activates the push-to-start button. When the key is moved away from the vehicle, the doors lock and the push-to-start function is deactivated. The immobilizer key transponder is powered by a small battery.
Each immobilizer key emits a unique transponder signal, which must be programmed into the on-board controllers for them to recognize it. The ECM/PCM and security control module are responsible for engine starting, while the body control module (BCM) handles door and trunk lock/unlock functions.
When either the ECM/PCM or an immobilizer key is replaced, it must be programmed. If the ECM/PCM fails to recognize an immobilizer key during vehicle entry or start-up, code P0633 will be stored and the malfunction indicator lamp (MIL) may illuminate. The ECM/PCM compares the immobilizer key transponder signature with other controllers each time the security system is activated and the self-test function is energized.
Photo of a PCM with the cover removed:
What is the severity of this DTC?
A stored code P0633 should be considered severe. If the controllers fail to recognize the immobilizer key, important functions such as engine start-up and door unlocking could potentially be disabled.
What are some of the symptoms of the code?
Symptoms of a P0633 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P0633 troubleshooting steps?
Due to the sensitive nature of certain parameters that must be programmed into the related controllers (such as VIN and mileage), reprogramming equipment access should be limited to qualified personnel. If controller replacement is necessary, successful repair will be impossible without the means to reprogram the controller in question.
Although the stored code P0633 may be attributed to controller failure or a programming error, it is most likely caused by a problem with the immobilizer key or transponder battery.
To accurately diagnose a code P0633, a diagnostic scanner and reliable vehicle information source are required. Use the vehicle information source to search for relevant technical service bulletins (TSB) that match the vehicle make and model, exhibited symptoms, and the stored code. This will help guide you towards a correct diagnosis.
Note: There are multiple known TSBs, one for Dodge/Chrysler/Jeep vehicles #08-030-06, and one for GM vehicles #PIT4660B.
By connecting the diagnostic scanner to the vehicle diagnostic port, you can determine if the ECM/PCM (and other controllers) is recognizing the immobilizer key. This information is typically displayed as a simple yes or no without specific transponder details. If the ECM/PCM does not recognize any immobilizer key, suspect a dead battery in the key fob or the use of an incorrect immobilizer key.
If the scanner display shows an inadvertent immobilizer key yes signal, suspect that the ECM/PCM has been replaced without being programmed to match the vehicle. If this is not the case, ECM/PCM failure or a programming error may be the cause.
In some cases, reprogrammed aftermarket replacement controllers and immobilizer keys may be available. If this is an option, you will need to provide the parts vendor with the vehicle’s mileage and VIN, as well as a secondary (factory programmed) immobilizer key.
Replacement of any vehicle security system component or controller usually requires system reprogramming.
