As you dont own equipment to see the sensor inputs at the ECU - it will become very frustrating.

You need to find a small oscope to see if you are seeing signal at the ECU itself from any sensor which is throwing errors, This is how these cars were repaired when they were common.

The mercedes diag software for this can show you this data too.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)