Question

2012 Mercedes Benz GL450 V8 with code P0721, what repair is required for this problem?

Answer 1

P0721 this code will give you a limp home mode condition, what is at fault here is the RPM sensor,to resolve this code condition you will need to replace the transmission control unit which is attatched to the electrohydraulic controller unit  (EHS).

Answer 2

P0721 MERCEDES-BENZ Code - Output Speed Sensor Range/Performance

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