OBC reset is just the dashboard nothing to do with engine/transmission. It will reset clock and all driving feedback like mpg/dte/fuel etc. The main point of using is to get the fuel gauge to read correctly after a fix since it uses a long term average for calculating the value for the dash needle.

I had a defect in my float sensor. On one side it read empty for a while. I didn't notice because I was only filling 1/2 tanks. Then I went on a road trip and when I filled up the needle went only to ²/₃ tank.

When I fixed the level potentiometer it still wouldn't read a full tank until I hit test 21. It then instantly showed a full tank. I'm sure that given enough time it would eventually read correctly without 21 reset but best to reset it you ever work on fuel sending unit.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)