DTC U0402 00: Abnormal Message From Transmission/Transaxle: Notes

WARNING: This page is about a different car, the 2014 Mazda 3. However, it is still accessible from the selected car via links, so may be relevant.

DTC U0402 00 DETECTION CONDITIONS AND POSSIBLE CAUSES (DYNAMIC STABILITY CONTROL)

DTC	U0402:00	Abnormal message from transmission/transaxle
DETECTION CONDITION	The DSC HU/CM received error signals from the transmission/transaxle for 1 s or more with the ignition switched ON (engine off or on).
FAIL-SAFE FUNCTION	Illuminates the TCS/DSC indicator light and smart city brake support (SCBS) indicator light (amber)^1 . Tire pressure monitoring system warning light^1 illuminates after flashes. Inhibits the TCS, DSC, hill launch assist (HLA), TPMS^1 , and smart city brake support (SCBS)^1 controls. ^*1 : If equipped.
POSSIBLE CAUSE	The transmission/transaxle could not send a normal signal temporarily. (DTCs are stored in the TCM.) Transmission/transaxle malfunction DSC HU/CM malfunction
SYSTEM WIRING DIAGRAM	Not applicable