For owners of the Lexus LS400, particularly earlier models (Mk1, Mk2, Mk3), a common issue revolves around the Engine Control Unit (ECU). Leaking capacitors within these ECUs can lead to a range of malfunctions, and in severe cases, irreparable damage to the circuit boards, rendering the ECU unusable. While this problem is more frequently observed in older models, it can also affect Mk4 LS400s, likely due to the age of the components.
For Mk1/2/3 LS400s, replacing a faulty ECU with another unit, ideally refurbished with new capacitors, is typically straightforward. However, Mk4 LS400 ECUs introduce a layer of complexity due to their immobilizer systems. If you’re dealing with a Mk4 and don’t possess the original master key for the replacement ECU, simply swapping it out will prevent your car from starting. This is because the Mk4 ECU incorporates an EEPROM (Electrically Erasable Programmable Read-Only Memory) chip, often IC900, which stores crucial immobilizer and key information.
When replacing a Mk4 ECU, the car’s immobilizer system will recognize that the replacement ECU doesn’t contain information about your original keys. Consequently, the engine will be immobilized. Fortunately, there are a couple of established methods to address this immobilizer challenge and ensure your replacement ECU functions correctly with your vehicle. These methods often involve working with Car Ecu Dump Files, which are essentially copies of the data stored within the ECU’s memory chips.
One approach, suitable for those with soldering skills or access to someone who does, is Method 1: EEPROM Chip Swapping. This involves physically removing the 8-pin immobilizer EEPROM chip (IC900) from your original, functioning ECU and carefully soldering it into the replacement ECU. By transferring the EEPROM, you’re essentially transferring the key information, so the replacement ECU will recognize your existing keys.
Method 2 offers a software-based solution: EEPROM Reprogramming. This method is more intricate and delves directly into manipulating car ecu dump files. It involves reprogramming the EEPROM chip (IC900) on the replacement ECU. The process typically requires removing the chip from the circuit board for optimal access, although in-circuit programming might be possible with specific tools. Using an EEPROM programmer connected to a computer, you would first download the current data from the EEPROM. This downloaded data is your car ecu dump file.
The next step is to edit this car ecu dump file using specialized software. The goal is to “virginize” the key entries, essentially zeroing out the stored key codes, except for the valet key lockout code. This process prepares the immobilizer system in the ECU to enter programming mode, ready to learn new key codes. After editing, the modified car ecu dump file is then written or uploaded back to the EEPROM chip using the programmer. Finally, the EEPROM chip is resoldered onto the ECU circuit board.
Upon reinstalling the reprogrammed ECU, a key programming procedure needs to be performed. This usually involves a sequence of steps to program each key, typically up to three keys, where the first two are designated as master keys and the third as a valet key.
Alternatively, and potentially a more straightforward approach within Method 2, is to obtain a car ecu dump file from a working ECU of the same model. This “good” dump file can then be written directly to the EEPROM of your replacement ECU. This bypasses the need for manual data editing and can be a faster solution if a compatible dump file is available.
For those considering Method 2, selecting the correct EEPROM programmer is crucial. It needs to be compatible with the 93xx/95xx series 5V EEPROMs commonly used in automotive ECUs. Researching and choosing a reliable programmer is an essential step before attempting EEPROM reprogramming.
While swapping the EEPROM chip (Method 1) is arguably simpler for those without EEPROM programming experience, reprogramming (Method 2) offers a more versatile solution, especially when dealing with used ECUs or when you want to avoid physically modifying your original ECU. However, both methods require a degree of technical understanding and caution. It’s always advisable to seek professional assistance if you are not comfortable working with electronic components or software-based ECU modifications.
