P0633 – Immobilizer key not programmed -ECM/PCM

By Bojan Popic (Contact Me)
Last Updated 2023-02-20
Master Mechanical Engineer
CodeFault LocationProbable Cause
P0633 Immobilizer key not programmed -ECM/PCM
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Table of Contents

  1. What Does Code P0633 Mean?
  2. Where is the P0633 sensor located?
  3. What are the common causes of code P0633 ?
  4. Get Help with P0633

What Does Code P0633 Mean?

P0633 is a generic code trouble code defined as Immobilizer key not programmed -ECM/PCM. It will be triggered when the signal coming from the key doesn’t match what the PCM (Powertrain Control Module) expects to get.

To understand the meaning of the code, we’ll first have to explain what the immobilizer key is and what it does. Most modern cars have one or more anti-theft functions integrated into their electronics, which prevent them from being entered into or stolen easily. Some of the features include remote locking, an alarm, and, most importantly, the immobilizer. This device is usually integrated into the vehicle’s PCM and prevent’s it from being turned on until it receives an appropriate code. This code, which acts as a password, is, in most cases, digitally inscribed into the car keys.

Where is the P0633 sensor located?

Although its configuration could differ depending on the vehicle, most car immobilizers work on the same principle and have similar components.

First, a key or a fob, which is used to unlock and start the car, has a microchip inside it. This chip contains a unique code, which is recognized by the car’s immobilizer system when in its proximity.

Next, there’s an antenna, which communicates with the key and the microchip inside it and picks up the signal from it. In cars where the key is turned inside the keylock, this antenna is usually integrated into the ignition barrel or switch. If a vehicle has a push-start button, the antenna will most likely be somewhere inside the dashboard. In most cases, this will be behind the slot into which the key fob is inserted before starting the car.

Lastly, there’s an immobilizer control unit, which is a computerized module responsible for controlling this anti-theft system. It compares the signal or code, the antenna picked up from the key to those it expects to receive. And if these are a match, it sends a signal to the PCM, saying the engine can be turned on.

What are the common causes of code P0633 ?

As said, the P0633 trouble code is always caused by issues with the immobilizer system, which has only several components. This narrows down the list of potential causes and makes troubleshooting easier. 

While specific causes of the P0633 trouble code can vary depending on the make and model of the vehicle, some of them are more common than others. 

Faulty key

For a start, if the key is damaged, the immobilizer may fail to retrieve a signal from it. This, however, is not likely to happen if the battery inside the key is flat, as most transponder chips inside them are passive. Or, in simple words, they don’t need a power source to generate a signal. But things like mechanical damage or electrical shorts may destroy the transponder chip and code inside it. Using a spare key may confirm if this is the case. 

Mismatched or malfunctioning immobilizer system components

To know which access codes to generate and expect, the immobilizer, PCM, and all car keys have to be paired up. So, if any of them fails and gets replaced, it also must be programmed. During this, an appropriate set of codes is electronically inscribed into a newly-fitted component. This, however, can only be done using specialized programming equipment. 

Wiring issue 

The immobilizer, PCM, and external antenna are all connected with wiring, which may get broken or damaged. If this happens, the signal from a matching component won’t get through the rest of the system. 

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