DTC U0402-00: Abnormal Message From TCM: Notes

WARNING: This page is about a different car, the 2018 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

DTC U0402:00 (DYNAMIC STABILITY CONTROL (DSC)) DETECTION CONDITION AND POSSIBLE CAUSE

DTC	U0402:00	Abnormal Message From TCM
DETECTION CONDITION		Correct data cannot be received from the TCM with the ignition switched ON (engine off or on).
FAIL-SAFE FUNCTION		Refer to "Fail-safe Function Malfunction Contents". (See DTC TABLE (DYNAMIC STABILITY CONTROL (DSC)) .)
POSSIBLE CAUSE		The TCM could not send a normal signal temporarily. (DTCs are stored in the TCM.) Transmission/transaxle malfunction TCM malfunction
SYSTEM WIRING DIAGRAM		Not applicable