Fix P0633: Mechanic’s solutions that WORKED

The OBD2 code P0633, specifically titled “SKIM (Sentry Key Immobilizer Module) Secret Key Not Stored in PCM (Powertrain Control Module),” is a unique diagnostic trouble code that can be somewhat perplexing.

This code is set when there is a communication gap between the vehicle’s immobilizer module and the PCM, indicating that the secret key data necessary for starting the vehicle has not been programmed into the PCM. This situation can occur after replacing the PCM or when there’s a fault in the vehicle’s anti-theft system.

P0633 quick overview

Meaning	P0633: SKIM Secret Key Not Stored in PCM
Is it serious?	Yes, it can prevent the vehicle from starting or functioning properly.
Possible causes	– Newly installed PCM not properly programmed with secret key data – Communication errors between the PCM and the immobilizer module – Faulty PCM or immobilizer module
How to diagnose?	Use a compatible scan tool like WiTech or Star Scan for programming and diagnostics. Verify the PIN number and attempt reprogramming using alternate procedures if available. Check communication between PCM and WCM/SKIM for errors. Reset and reinitialize the immobilizer system if necessary. Replace faulty hardware such as the PCM or WCM if diagnosed.

How to fix P0633 – learn from mechanics

I looked into P0633 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Jeep

Vehicle information 2008 Jeep Wrangler X 3.8L

Issue + repair history

• Replaced and programmed PCM using WiTech.
• Unable to input pin number into WCM to program secret key information into PCM.
• Error message “Unable to retrieve WCM/WIN unlock results. Procedure failed. Internal error occurred.”
• Confirmed correct pin number.
• Vehicle starts and runs but sets P0633 code in PCM.

Other OBD2 Codes + Test Results

• P0633: SKIM Secret Key Not Stored in PCM

Mechanic suggestions

• Use Star Scan if available, as WiTech may give pin errors.
• Try “alternate procedures” at bottom of the screen which uses the familiar Star Scan looking procedure.

Final fix Resolved communication issues with WiTech/Star Mobile by backing up to an earlier version, then reinstalled the newest version to enter the pin successfully.

Case #2: Chrysler

Vehicle information 2012 Chrysler Town & Country Touring L 3.6L

Issue + repair history

• Programmed a new PCM and entered pin for the secret pass key.
• Unable to get pin registered, resulting in persistent P0633 code.
• Vehicle runs great with no problems.
• Code does not cause check engine light to come on.

Other OBD2 Codes + Test Results

• P0633: Secret key pin not in PCM

Mechanic suggestions

• Run PCM replaced routine in the WCM.
• Erase all DTCs and insert secret key information into PCM using module programming procedure.
• Enter pin code in WCM miscellaneous functions, select PCM replaced, and cycle key off and start vehicle.
• Use WiTech 2 for correct procedure.
• Ensure normal programming of PCM software, VIN verification, and mileage verification.
• Consider BCM configuration alignment if applicable.

Final fix After multiple attempts and seeking assistance from a training instructor, successfully entered the pin number with the engine running, which allowed the PCM to accept the pin number and clear the P0633 code.

Case #3: Chrysler

Vehicle information 2006 Mitsubishi Raider LS 3.7L

Issue + repair history

• The vehicle was broken into, lost keys.
• Replaced WCM (Wireless Control Module).
• Vehicle sets P0633 code and doesn’t start.
• Transponder coil not being excited.
• No codes in WCM module, only PCM has P0633.
• New key and new WCM installed, programming unsuccessful.

Other OBD2 Codes + Test Results

• PCM code: P0633

Mechanic suggestions

• Check if the antenna powers up on key turn to the run position.
• Ensure communication with WCM.
• Perform ECM reset.
• Use diagnostic scan tool for SKIS initialization and key programming.
• Retrieve unique four-digit PIN code for SKREEM initialization.
• Use Secured Access Method for SKREEM initialization.
• Transfer Secret Key code to new SKREEM from PCM during replacement.
• Ensure proper completion of SKIS initialization to allow existing Sentry Keys to be programmed into the new SKREEM.

Final fix PCM was found to be bad and not originally equipped with theft. Replacing the PCM resolved the issue.

Diagnostic Step	Brief Explanation
Use appropriate diagnostic tools	Utilize WiTech or Star Scan to program the PCM and troubleshoot communication issues.
Verify and re-enter PIN	Confirm the correct PIN number and use alternate procedures for entering it if initial attempts fail.
Communication check	Ensure proper communication between PCM and WCM/SKIM, looking for any signs of malfunction.
Reset and reinitialize systems	Perform necessary resets and reinitialization of the immobilizer system for proper key recognition.
Replace and reprogram PCM/WCM if needed	In cases where hardware is faulty or not properly equipped, replace and ensure correct programming.

Addressing a P0633 code can involve intricate steps that require specialized diagnostic tools and knowledge of the vehicle’s anti-theft system. While some issues can be resolved through reprogramming or resetting systems, others may necessitate hardware replacement. For vehicle owners, understanding the importance of professional diagnostics and programming in these scenarios is crucial, and seeking experienced mechanic assistance is often the best course of action.