Problem:
I’m working on a VW Polo 6R with a Delphi DCM 3.7 engine computer (ECU). Normally, tools like Foxflash or KESS can read this ECU through the car’s OBD port, but since the ECU was taken out of the car, I tried reading it on the bench using a Godiag GT100 breakout box connected like an OBD port. Foxflash still couldn’t read the memory.
Then I tried using Scanmatic + PCMFlash. I was finally able to read the ECU with the Godiag setup, but I can’t write anything back to it—reading works, writing doesn’t.
I also tested with OBDSTAR DC706 and Xhorse Multi PROG, but neither supports this specific ECU for VW Polo (even though they work with the same DCM 3.7 in Kia/Hyundai/SsangYong vehicles).
My question is: If this ECU can be read via OBD when it’s in the car, why can’t I read or write to it on the bench using an ECU box? The tool detects the ECU, but it can’t read or write. Is there a solution?
Solution:
The issue is that the immobilizer is still active. This ECU requires a connection to the immobilizer system (through the Body Control Module) to allow full access—even for reading and writing.
When the ECU is on the bench, the immobilizer isn’t connected, so it blocks access.
You have a few options:
Read/write it via OBD when the ECU is installed in the car (with immobilizer connected).
Use JTag or Boot mode with tools like KESS3, Foxflash, or KT200.
KESS3 has been known to work via OBD. Foxflash and KT200 can also do it over OBD.
So on the bench, unless you simulate or bypass the immobilizer, you’ll need to use JTag or Boot mode.
