Speaking from experience, clean the wiring harness plug and transmission harness socket first. Shorted out pins produce false error codes. Going through a car wash was enough to make my transmission go into fail safe because of debris that built up in the connector.

2002 X5 3.0 331,000 miles
2014 428i 29,000 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - Under restoration