BMW 523i with engine code N52B25A crank no start

Hello everyone, my name is Arne. I am a workshop manager in a Bosch car service garage in Belgium. (new member). this week i had BMW 523i with engine code N52B25A in the workshop from another garage.
Symptoms are, crank no start.

The garage had already replaced the in-tank fuel pump and the cranshaft sensor.
without succes......(parts cannon...)
when i scanned the car there where verious error codes presenet in the DME (ecm for bmw). Some of these faults where cranshaft sensor errors, throttle valve errors, and codes for al the temprature sensors on the engine (ect, ips,...) an many orther fault codes.

My first checks were is there spark, fuel and can the engine breath.....
after checks, the injectors were not controlled an there was no spark.
There was also a missing crankshaft signal errror code in the fuel pump module (EKPS).
When i checked data, i saw both coolant temprature sensors and the air intake temprature sensor showed a value of -48 degrees (same as unplugged), also no RPM value.
After looking at a wiring diagram I noticed that everything on 5V reference worked but nothing worked on the 12v system of the engine computer.
The garage owner told me that they had checked grounds and powers to the DME. But it soon came to light that the power supplys and grounds were indeed present when you backprobed the plug, but not if you did the measurement on the plug side. When i pulled the plug off the DME i saw it immediately.... and there it was, corrosion on the pins. so power was advailable if you backprobed it but not at the tops of the pins on the computer. With the ignition on the voltage was good, when cranking the voltage dropped. I measured a voltage drop o 10,5V when cranking.
So lesson learned always visual check plug and pin side, and test the circuit under load.
I cleaned the pins and the connector. After plugging everything back in, the car started immediately. a no parts fix.

i diagnose vehicles every day, it's my job. and will try to share a diagnosis with you every day, so we can al learn about it.
Sorry for the long text an bad english. I'm Belgian and my English is basic.

good evening everyone.....chears.
 

great diag and THANKS for sharing Amigo