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

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Mazda 6 Service Manual: Obd drive mode
Performing the Drive Mode inspects the OBD system for proper operation. The Drive Mode must be performed to ensure that no additional DTCs are present. During Drive Mode, the following systems are inspected: - Oxygen sensor (HO2S) - Oxygen sensor heater - Catalytic converter (TW ...

Mazda 6 Service Manual: Foreword
Caution When the engine does not start or stalls and the following DTCs are not indicated, go to engine symptom troubleshooting. Note When the immobilizer system is defective, the engine cannot be started. If engine condition is normal but light stays on, inspect for short circ ...