PCR 2.1 immo off guide

How to immo off simos pcr 2.1

Understanding the Simos PCR 2.1 ECU

The Simos PCR 2.1 (often just called SIMOS 2.1) is an engine control unit (ECU) developed by Siemens/Continental for Volkswagen Group vehicles. It’s found in many VW, Audi, Seat and Skoda models equipped with 1.6 TDI engines. In fact, Simos PCR 2.1 belongs to the fourth-generation immobiliser family (WFS4/IMMO4) used by VAG. The ECU uses a TriCore TC1796 microcontroller and includes both flash memory (for the engine software) and an EEPROM (for data like key codes). Because SIMOS is a Continental (Siemens) OEM unit, it replaced older Siemens Med17 or VDO ECUs in many diesel cars around 2009–2014. For example, cars like the VW Golf VI, Passat B7, Polo 6R, Audi A1/A3 8P (1.6 TDI) and Skoda Octavia II commonly use SIMOS PCR2.1.

Simos PCR 2.1 handles engine management functions (fueling, boost, etc.) but also tightly integrates VAG’s immobiliser (“Wegfahrsperre”) system. The immobiliser data – including the vehicle identification number (VIN), PIN code and security bytes (Component Security, or CS) – are stored on the ECU (typically in the EEPROM). When the car starts, the system checks that the key’s transponder code matches the ECU’s stored PIN and CS. If they don’t match, the ECU locks the engine (no start) as a security measure.

Key Point: The SIMOS PCR 2.1 ECU is a WFS4/IMMO4 unit used in VW 1.6 TDI cars. It contains both the engine map and the immobiliser data (VIN, PIN, CS) on-board.

Understanding the hardware is helpful. A typical PCR 2.1 unit has a green circuit board inside a metal housing, with connectors to the car’s wiring harness. The heart of the board is the Infineon TriCore TC1796 microcontroller (the brain). For many operations, technicians connect to it via the round 176-pin connector (often labeled C167) or via solder points if opened. This microcontroller contains the bootloader, which is used for reading/writing the ECU’s full data. To modify the immobiliser, we ultimately unlock and access this TC1796 controller.

Simos PCR 2.1 is different from some earlier PCR series like PCR 2.0 or 2.5, and from older Siemens VDO/Med17 units. Its locking mechanism (IMMO4) is more secure: you cannot simply “clone” the data from one PCR2.1 ECU to another without addressing the immobiliser. Simply transferring the EEPROM isn’t enough, because the TC1796 keeps a security lock. In practice, even if two PCR2.1 ECUs have the same part number (e.g. 03L 906 023), you usually need to disable (turn off) the immobiliser function if you swap ECUs between cars or use a donor ECU.

Image of a simos ECU (Figure above). The PCR 2.1 ECU uses a TriCore TC1796 CPU and contains both engine software and immobiliser data. Disabling the immobiliser requires special boot‑mode access to this unit.

How the VAG Immobiliser (IMMO) System Works

Before performing IMMO OFF, it helps to understand how VAG’s immobiliser system operates on PCR 2.1. Volkswagen/Audi immobilisers (called Wegfahrsperre or WFS) tie the car’s ignition system to the transponder-equipped keys. With a SIMOS PCR 2.1 (WFS4) system, key data is stored on the ECU and the dashboard (cluster), and proper matching is required for engine start. Key information includes the 4-digit PIN and a 4-byte component security (CS) value. These values are programmed into the ECU’s EEPROM when the car is first coded. Every time the ignition is turned on, the ECU checks that the coded PIN/CS match what’s in the cluster (and the transponder key). If the data does not match (for example, if the ECU has been replaced without reprogramming), the engine is disabled.

Technically, the PCR2.1 ECU’s firmware contains an IMMO routine that will prevent injection or starter engagement if the immobiliser is active. The ECU’s flash typically includes an immo disable block or flag. Disabling IMMO (IMMO OFF) involves either erasing or patching this block so the ECU no longer checks for the matching key code. In other words, an IMMO OFF patch effectively removes the security check code from the software.

An important point: PCR 2.1 uses CAN bus for communication (to verify keys and PIN). It has separate memory areas for the engine tune (flash) and for coding information (EEPROM). Key details are normally stored in the EEPROM at specific addresses. Many tools (like the WebOctopus IMMO Editor) allow reading the VIN/PIN/CS/Powerclass from these files and editing them. However, simply editing these values won’t allow engine start unless the ECU itself is unlocked for writing and the immobiliser check is bypassed.

Did you know? The term “Power Class” on VAG ECUs is the numeric identifier of the car model/engine the ECU is coded to. PCR2.1 units include the Power Class in their coding data. IMMO OFF tools often let you transfer the power class along with VIN/PIN data when cloning an ECU.

In summary, performing IMMO OFF means we either remove the requirement for the original PIN/CS or override that logic entirely. This is usually done by: (a) reading out the ECU’s binary data (flash and/or EEPROM) via boot mode, (b) running a special software patch that clears or neutralizes the immobiliser section, and (c) writing the modified data back. After doing so, the ECU will accept any key (or effectively have no key lock), and the engine can start without immobiliser matching.

Why Perform an IMMO OFF on PCR 2.1?

Disabling the immobiliser on a PCR2.1 ECU is rarely for convenience alone – it’s typically done for practical reasons. Here are common scenarios where a PCR 2.1 IMMO OFF is needed:

ECU Replacement or Swapping: If a PCR2.1 ECU has failed (water damage, chip error, etc.), replacing it with a used or new unit will trigger an immobiliser mismatch unless IMMO OFF is done. For example, swapping in a donor ECU from a similar car (e.g. a 2012 VW Golf 1.6 TDI) will fail to start unless the immobiliser lock is disabled. Data Corruption or Cloning: In some cases, an ECU might lose its coding (VIN/PIN) due to a write error or corruption. If a tech tries to “clone” the EEPROM from a damaged ECU into a fresh unit, the SIMOS PCR2.1 often still detects a mismatch because it ties the pin to the ECU’s unique identifiers. Performing IMMO OFF allows cloning the ECU without worrying about the VIN/PIN mismatch. Engine Swaps and Tuning: Enthusiasts sometimes swap a 1.6 TDI engine (with PCR2.1) into a different VW body or do heavy tuning. Disabling the immobiliser ensures that an ECU from any donor car will run the engine without immobiliser intervention. This can simplify engine swaps where key adaptation might be tricky. Service Failures: Occasionally, cars come with immobiliser faults (blown transponder, etc.). A quick diagnostic might be an IMMO OFF to rule out ECU/key mismatches. Professional services may offer a temporary or permanent IMMO OFF as a quick fix for no-start issues.

It’s worth noting that performing IMMO OFF is generally intended for legitimate repairs – such as fixing a dead ECU – rather than for illegal use. Dealers or trusted workshops will often charge for this procedure. For example, IAS Automotive offers a PCR2.1 IMMO OFF service, requiring the ECU’s boot-mode dump (TC1796 file) and then applying a custom patch. They highlight that they do not use generic, mismatched files; each ECU is handled individually so other vehicle configurations remain untouched. This ensures the ECU still behaves correctly except for the removed immo lock.

By disabling the immobiliser, you regain full control: the car will start normally even if the ECU’s VIN/PIN don’t match the keys. After IMMO OFF, technically the ECU is “immobiliser‑free,” meaning it won’t check keys at all. Keep in mind that after this operation, if the car is ever sold or re-serviced, it’s good practice to document that the ECU no longer has an active immobiliser.

Essential Tools & Software

Disabling a SIMOS PCR 2.1 immobiliser requires specialized equipment. Below is an overview of the hardware and software tools commonly used:

Hardware Programmers: You’ll need a flash tool capable of working with PCR2.1’s TriCore TC1796 microcontroller. Common choices include KESS V2 (Alientech Ksuite), K-TAG (Alientech), MPPS, Autotuner, FGTech Galletto (V54), Magic X-17, OBDSTAR DC706, XDJs, etc. All of these can read/write PCR2.1 data, but note that most require bench mode to unlock the ECU for reading or writing. The Magic X-17 is notable because it reportedly supports direct OBD (no bench) communication with PCR2.1 (as of recent versions). Boot/SSM Cables: Because PCR2.1 ECUs often need a boot mode connection, you will require a TriCore boot cable. The Infineon cable model SSM 144300T111 is standard for PCR2.1 bench mode. This 12‑pin cable (also called TriCore cable) connects between the ECU and the programmer, providing power, ground, CAN lines, and debug (SSM) signals. Without this cable (and sometimes an external 12 V supply), you cannot communicate with the locked microcontroller.
Figure: An Infineon SSM cable (144300T111) used for PCR2.1 ECU bench-mode connection. This specialized cable interfaces the ECU’s TC1796 controller to the programmer for reading/writing. Immo-OFF Software/Services: There are sofware tools specificaly designed to disable the immobiliser in a PCR2.1 ECU. For example, CK Decode is an online service where you upload the full ECU dump and it patches the immobiliser section.

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