Mazda 6 Service Manual: No.20 noise occurs at idle when vehicle is stopped in all positions/ranges

No.19 excessive shift shock on torque converter clutch (tcc)

No.21 noise occurs at idle when vehicle is stopped in d, s, l ranges, or in r position

Other materials:

Mazda 6 Service Manual: Dtc c1955, c1956
Caution When attaching the tester lead to the DSC HU/CM connector the SST (49 G066 004) must be used. Diagnostic procedure ...

Mazda 6 Service Manual: Disconnection of the negative battery cable
Before beginning any work, turn the ignition switch to LOCK position, then disconnect the negative battery cable and wait for more than 1 minute to allow the backup power supply of the SAS unit to deplete its stored power. Disconnecting the battery cable will delete the memories of the ...