Sonar MB1240 is unable in the Pixhawk 4 operations

I use original Pixhawk4 at present, the firmware edition am 3.6.10, uses the Sonar is MB1240 carries on the connection by I2C A port , and makes the hypothesis according to the official method, changes RNGFND_MAX_CM = “700” and RNGFND_TYPE = “2” two parameters in Mission Planner, but the sonarange value still is 0, ask whether I do have the omission important step? Please help me, thanks you.

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