Problem
During boot glitch unlocking on a Bosch MG1CS028 ECU from a Land Rover Defender P400, Flex ECU programmer may instantly disconnect from the PC USB port and request an ignition reset. This issue stems from a ground pinout mismatch on specific ECU hardware revisions and incorrect glitch line resistance.
Root Cause Analysis
- Short Circuit via GND Pin:The default Flex pinout places the black GND wire in a secondary connector slot. On certain MG1CS028 hardware revisions, this causes a short circuit, forcing Flex tool to trigger a hardware USB shutdown.
- Weak signal control:A standard single 2.2 ohm resistor on the glitch probe line provides insufficient signal damping to achieve a stable unlock pulse.
Step-by-Step Solution
1.Relocate the GND Cable: Move the black GND wire from the secondary connector slot to the primary power block in the top-right pin array (referencing AutoTuner connection layout).
2.Adjust Glitch Resistance to 5 Ohms: Replace the 2.2 ohm resistor with a 5 ohm resistance setup (wire two 10 ohm resistors in parallel if a single 5 ohm resistor is unavailable).
3.Execute Boot Unlock: Run the boot glitch process in Flex software. The unlock will complete without triggering a USB disconnect.
4.Restore PCB & Perform Bench Read: Resolder the original surface-mount resistor across the two board pads, switch to standard bench mode, and perform a full backup read.
Important to know:
To complete the process successfully, use the ground pin location from AutoTuner wiring diagram and add a 5-ohm resistor to the glitch line. Keep both the ground pinout and signal resistance in mind when working on this ECU.
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