Mechanic Wiki: BMW CAS4/CAS4+ Module Replacement Guide Using LAUNCH X431 XPROG3

Learn how to replace a BMW CAS4 or CAS4+ module step by step using the LAUNCH X431 XPROG3. Includes EEPROM cloning, key learning, and ELV initialization.

Published: May 24, 2026

Quick Answer

Replacing a BMW CAS4 or CAS4+ module requires you to read the original module’s EEPROM data, write that data to a new or used module, then perform a key learning and steering lock initialization using a diagnostic tool. The LAUNCH X431 XPROG3 simplifies this by combining a full diagnostic scanner with a dedicated chip programmer. You do not need to replace the engine DME if you correctly clone the CAS data. The core steps: backup original EEPROM, remove and erase the new MCU, write the backup file, solder everything back, and synchronize the module with the vehicle via the X431.

Understanding the BMW CAS4 and CAS4+ Module

Before you pick up a soldering iron, it’s critical to understand the hardware differences between CAS4 and CAS4+. Get this wrong, and you risk bricking the module.

CAS4 vs. CAS4+: Physical Differences

The CAS4 (Car Access System, generation 4) was introduced around 2007 and appears in many E-series models like the E90, E60, and E70. The CAS4+ came later (around 2010) and is found in early F-series cars like the F10 and F25. The two modules look similar but have different connector layouts and chip configurations.

CAS4 commonly uses a 5M48H or R5F364A microcontroller (MCU).
CAS4+ often uses a 1M35S or R5F7253x MCU, and the EEPROM is usually integrated into the MCU itself.

Physically, CAS4+ has a more compact housing and a different pinout for the main connector. If you try to use a CAS4 module in a car designed for CAS4+, the connectors won’t match — and even if you repin them, software compatibility is a gamble.

What the CAS Module Does

The module controls more than just the ignition button:

Immobilizer system: It communicates with the key transponder and the engine DME to verify a valid start request.
Steering lock (ELV): It activates and releases the electronic steering lock when the key is recognized.
Key recognition: It reads the rolling code from the key fob.
Transmission interlock: It prevents shifting out of Park without the key present.

Common Failure Symptoms

When a CAS module fails, you’ll notice one or more of these issues:

No crank and no dash lights when pressing Start/Stop.
Key not recognized (you get a “No Key” message).
Steering wheel stays locked.
Transmission stuck in Park.
Intermittent starting problems that get worse over time.

If you’re seeing these symptoms, especially after a battery drain or water intrusion behind the glovebox, the CAS module is the likely culprit.

Required Tools and Preparation

Having the right tools on hand before you crack open the module saves you from awkward mid-job hardware store runs.

Main Device: LAUNCH X431 XPROG3

This is the star of the show. The XPROG3 is both a full diagnostic scanner and a dedicated chip programmer. For this job, you’ll use both functions:

Programmer software to read and write EEPROM data from the MCU.
Diagnostic software to perform key learning and ELV initialization after the module is installed.

Make sure your XPROG3 has the latest software update. LAUNCH regularly adds new vehicle coverage and bug fixes. Without the latest update, you might not see the correct CAS4/CAS4+ options.

Hardware You’ll Need

Item	Purpose
EEPROM adapter board (included with XPROG3)	Connects the MCU pins to the programmer
SOP8/SOP16 test clip (or soldering wires)	Temporary connection for reading the original MCU
Fine-tip soldering iron (e.g., TS-100 or Hakko)	Solder wires to MCU pins or desolder for socket programming
Flux and desoldering wick	Clean joints and remove bridges
Magnifying lamp or microscope	Inspect tiny pins for shorts
ESD-safe mat and wrist strap	Protect sensitive electronics

Vehicle Preparation

Disconnect the battery negative terminal.
Wait at least 10 minutes for the capacitors in the vehicle’s electrical system to discharge. If you skip this, you risk shorting something when removing the CAS connector.
Locate the CAS module. In most BMWs, it’s behind the glovebox (remove lower trim) or under the dash on the driver’s side. Check your model-specific guide — the location varies between E90 and F10.

Step-by-Step Replacement Process

This process is for cloning the data from your original (faulty) CAS module to a new or used replacement module. I’ll assume you have already removed the original module and have a donor module in hand.

Step 1: Read and Backup the Original CAS Module

You need the original EEPROM data because it contains the VIN, the ISN (Individual Security Number), key data, and mileage.

Identify the MCU chip on the original module. It’s the largest IC, typically 32-pin or 64-pin. Look for markings like “R5F364A” or “5M48H” on top.
Connect the XPROG3 programmer to the MCU. You have two options:
- Use an SOP8/SOP16 test clip if the MCU is in a socket (uncommon for CAS modules — usually it’s soldered directly).
- Solder fine wires to the relevant pins (VCC, GND, SDA, SCL, etc.) and connect to the adapter board. Consult the XPROG3 wiring diagram for your specific MCU.
Launch the XPROG3 programmer software on your PC or tablet. Select BMW > CAS > CAS4/CAS4+ > Read EEPROM.
The software will prompt you to select the MCU type (e.g., for R5F364A, select the appropriate sub-menu). Follow the on-screen instructions.
Once the tool reads the data, immediately save the full binary file to your computer. Name it something unique like original_CAS4_VIN12345.bin. Keep a backup copy on a separate drive.

Warning: Do not interrupt power during the read process. A failed read can corrupt the module’s firmware.

Step 2: Prepare the Replacement Module

Now you need a donor module. It must have the same part number printed on the sticker (e.g., 6 924 152 or 6 931 628). The hardware revision must match, or cloning may fail.

If the donor module is used, you must first erase its existing data. Connect it to the XPROG3 the same way you did for the original. Select Read EEPROM first (to have a backup of the donor data), then select Erase or Blank Check (the option name varies by MCU). This wipes out the previous VIN and keys.
If the donor module is brand-new (blank), skip the erase step.

Step 3: Write Data to the Replacement Module

Keep the donor MCU connected to the XPROG3 programmer.
In the software, select Write EEPROM.
Browse and select the backup file you saved in Step 1 (original_CAS4_VIN12345.bin).
Click Write and wait. The process takes 30 seconds to 2 minutes depending on MCU size.
After writing, the XPROG3 will automatically verify the data. Do not skip this verification. A mismatch usually means a bad solder joint or wrong MCU selection. If verification fails, recheck your connections and try again.

Step 4: Reinstall the Module

Desolder the programming wires from the MCU (if you soldered). Clean the pads with flux and wick.
Double-check for solder bridges between pins using a magnifying glass.
Place the CAS module back in the vehicle. Plug in the connectors.
Reconnect the battery and wait 10 seconds for power to stabilize.

Post-Replacement: Key Learning and Initialization (X431 Diagnostic)

Even though the EEPROM data is cloned, the car’s chassis and steering lock may not synchronize immediately. You need to run a few routines with the X431 diagnostic unit.

Step 1: Connect the X431 Scanner

Power on the LAUNCH X431 and select Diagnosis > BMW > CAS.
The software will read the VIN from the module. It should match your original car.

Step 2: Initialize the Steering Lock (ELV)

Navigate to Special Functions > Steering Lock > Initialize.
Follow the on-screen instructions. The steering wheel lock will cycle — you’ll hear a clicking sound. Do not interrupt this procedure or turn the ignition off.
After initialization, the warning message “Steering lock malfunction” (if present) should disappear.

Step 3: Program the Keys

Go to Key Memory > Add Key / Program Key.
Insert the key into the ignition slot (or hold it near the steering column if your car uses a wireless fob).
The tool will prompt you to press the Start/Stop button. Do so.
The dashboard cluster should light up. The tool will confirm key learning is complete.
Repeat for each key you own (up to four).

Step 4: Test Start

Press the Start/Stop button without your foot on the brake to turn on ignition. The cluster should illuminate and show no warning lights.
Press the brake and press Start/Stop again. The engine should crank and start.
If the car starts, you’re done. If not, move to troubleshooting.

Troubleshooting Common Issues

Even experienced technicians hit snags. Here are the most common problems and how to fix them.

Issue: "ELV Not Coded" or "Transponder not read"

Fix: Re-inspect your solder joints on the MCU. A cold joint on the SDA or SCL line can prevent the diagnostic tool from reading the EEPROM correctly. Re-run the ELV initialization procedure — sometimes it just needs a second attempt.

Issue: "VIN Mismatch" between CAS and DME

Fix: This happens when the DME (engine module) was replaced at some point and the VINs don’t match. Use the X431 to navigate to Special Functions > CAS Alignment with DME or VIN Write to DME (options vary by model). Write the correct VIN to the DME using the tool.

Issue: Car cranks but no start

Fix: The problem is almost always a wrong ISN (Individual Security Number). If you accidentally wrote the donor module’s original data instead of your backup, the ISN won’t match the DME. Re-read your original backup and re-write it to the CAS. Also verify that the DME is communicating — try reading fault codes from the engine module.

Issue: XPROG3 says "Connection Failed"

Fix: Ensure the adapter board is seated firmly in the programmer. Try using the SOP8 test clip instead of the socket — sometimes the socket contacts are worn. Also, verify you selected the correct MCU type; picking the wrong one will cause communication errors.

Frequently Asked Questions (FAQ)

Can I use a CAS module from a different model BMW (e.g., E90 vs. F10)?

No. The part number must match exactly (check the white sticker on the module). The hardware revision and connector pinout differ between models. However, you can write a correct EEPROM backup to any module with the same part number, even if it came from another car of the same model.

Do I need to program the keys again after cloning?

Yes. Even though the EEPROM contains the key transponder data, the vehicle’s chassis needs to resynchronize the rolling codes. Use the X431 to perform a key relearn procedure after you install the cloned module.

Is it possible to replace CAS without the original module (if it’s completely dead)?

Yes, but it’s harder. You cannot clone data from a dead module. You must purchase a virginized module (blank or unlocked) and then use the X431 to perform a “CAS with DME Alignment” via the OBD port. This requires the DME to be readable. The tool will generate a new ISN and allow key programming, but the mileage will reset to zero unless you manually enter it.

Does the XPROG3 damage the MCU?

If you follow correct voltage settings and ground connections, it is safe. Most damage comes from poor soldering (bridging pins) or electrostatic discharge (ESD). Always work on an ESD-safe mat and use a grounded wrist strap.

Will this procedure reset the mileage?

The mileage is stored in the CAS EEPROM. If you clone the data from the original module, the mileage will remain exactly as it was. The XPROG3 cannot modify mileage during a standard read/write operation — doing so would require specialized decryption tools.

Final Checklist and Safety Warnings

Before you button up the car, run through this checklist:

Original EEPROM backup saved in two locations.
Replacement module has the same part number.
Soldered connections are clean with no bridges.
ELV initialization completed successfully.
Keys programmed (all of them).
Engine starts and runs without warning lights.
Steering lock releases and locks correctly.

Safety warnings to take seriously:

Always back up original data twice. One corrupted file and you lose the only copy of your ISN.
Never power the car while the CAS module is disconnected. This can trigger airbag or other fault codes that are difficult to clear.
Use a magnifying glass to inspect every solder joint. A single bridge can short the 12V supply line to a data pin and fry the MCU.
Test the new module on a bench (if you have a spare CAS connector and a power supply) before reinstallation. It’s much easier to debug on the bench than under the dash.

For a deeper dive into key programming and DME alignment, check out our guide on [link to related guide on BMW key programming with X431]. If you’re replacing the DME at the same time, read our article on [link to related guide on BMW DME replacement and alignment].

About the Author: Erwin Salarda is an Automotive Service Equipment Technician based in the Philippines, specializing in computerized automotive diagnostic equipment such as OBD scanners and wheel alignment systems. Since 2012, he has been actively providing technical support, equipment installation, troubleshooting, after-sales service, and hands-on training for automotive service equipment used by workshops and automotive professionals.

He has received specialized training from international suppliers and manufacturers, including Launch X431 in Shenzhen, China, Lawrence Engineering Company in Guangzhou, China, and 3Excel Wheel Alignment Company in Shenzhen, China. Through these trainings, he developed advanced expertise in automotive diagnostics, calibration, wheel alignment systems, and computerized automotive service technologies.

Erwin Salarda provides professional after-sales support and technical training for automotive diagnostic and wheel alignment equipment, helping clients maximize the performance and proper use of their tools and systems. His experience covers equipment setup, software updates, calibration procedures, troubleshooting, and operational guidance for automotive workshops and service centers.

With more than a decade of experience in the automotive equipment industry, Erwin Salarda continues to support automotive businesses by delivering reliable technical expertise and practical training solutions.

For inquiries and equipment purchases, please visit https://carlifterph.com/