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P0633 is a diagnostic trouble code (DTC) for "Immobilizer Key Not Programmed – ECM/PCM". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0633 code is triggered when the vehicle's PCM (Powertrain Control Module) or ECM (Engine Control Module) is unable to recognize the immobilizer key.
P0633 is cued when there is an internal malfunction or improper programming resulting in the PCM being unable to recognize the immobilizer key. The immobilizer is an engine component that prevents it from running without the proper electronic immobilizer key. The code indicates that the vehicle will not start because the proper key is not in use.
This code is most commonly caused by the following:
P0633 code typically cues the vehicle to illuminate a security lamp or key indicator that signals a "no start" will occur.
The P0633 is diagnosed with an OBD-II scanner, but the use of a digital volt/ohmmeter is also important in properly diagnosing this issue. The standard protocol begins with a visual inspection of the vehicle's wiring. Any problematic issues must be addressed, including replacing or repairing shorted, disconnected, damaged or corroded wires and connections. Components and fuses in need of repair or replacement are addressed at this time too.
The system is then re-tested and if the wiring is functioning properly, the mechanic may then connect the OBD-II scanner to the vehicle's diagnostic connection and document the codes and freeze frame data it contains. It is important to note any data or irregular issues that may have played a role in the code storage. Clear the code and attempt to operate the vehicle as this can indicate if that is the source of the problem. If it is not an electrical or wiring issue, it is likely that the PCM will need diagnosis and/or replacement. Typically this is more complex and requires the use of an Autohex or specialized scanner.
A mechanic must also assess any recent repairs, as any changes in a control module may lead to a reprogramming-related problem, and the P0633 code. It may also be necessary to use an auxiliary immobilizer key to test the current key's authority. If none of these yield results, the final test to perform is on the ignition cylinders as some vehicle types trigger this code when a cylinder is defective.
This is a very rare code with a very narrow number of causes. There are rarely misdiagnosis or mistakes to be made when this code is triggered.
This is a very serious issue because it prevents the vehicle from starting. Though helpful in the prevention of "hot wiring" and auto theft, when it is a malfunction in the immobilizer key or the PCM/ECM it locks down the engine and prevents the vehicle from operating at all. Unfortunately, diagnosis and resetting the codes is not always going to address the problem because reprogramming may be required. The vehicle ID, mileage, and any anti-theft settings may need to be reset before the vehicle can be operated.
The most common repairs required for the P0633 code are:
Never replace a PCM with a used component as this will not alleviate this issue. The OBD systems can function exclusively in the one vehicle, programming everything into the PCM or ECM, and then relaying and sharing information with other control modules through the CAN bus network. This code can mean a new PCM/ECM and that means reprogramming the unit to match the vehicle.
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