If your Flex ECU Tool instantly shuts down and drops its USB connection while trying to Boot Glitch a Bosch MG1CS028 ECU from a Land Rover Defender P400, here is why it happens and how to fix it on your bench.
What Causes the Shutdown?
1.Wrong GND Pin:
The default Flex harness layout uses a secondary GND pin that causes a short on some MG1CS028 board revisions.
This forces the tool to kill the USB connection to protect itself.
2.Low Glitch Damping:
The recommended 2.2-ohm resistor on the glitch line doesn’t dampen the signal enough for a clean unlock pulse.
Step-by-Step Bench Solution
1.Move the Ground Lead:
Do not use the default Flex GND pin.
Move the black GND wire to the main power block on the upper-right pin grid (use AutoTuner GND location instead).
2.Change Glitch Resistance to 5 Ohms:
Replace the 2.2-ohm resistor with a 5-ohm resistor on your glitch probe.
If you don’t have a 5-ohm resistor, wire two 10-ohm resistors in parallel.
3.Run the Unlock:
Start the Boot Glitch sequence in Flex software.
It will unlock cleanly without triggering a USB drop.
4.Restore Board & Read:
Resolder the factory SMD resistor back onto the PCB pads, switch over to standard Bench mode, and pull your full backup read.
Tech support:
Email: sales@OBDexpress.co.uk
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