What does code P1602 mean?

P1602 · MazdaPowertrain Control Module Communication Line To TCM Error, Immobilizer System Communication Error With Powertrain Control Module

P1602 on Mazda vehicles indicates that the powertrain control module (PCM) has detected a communication failure on the line connecting it to the transmission control module (TCM) or the immobilizer system. The PCM expects a regular handshake or data exchange with these modules, and when that signal is missing or corrupted, it stores this code and may illuminate the check engine light. This is a communication fault, not a direct sensor or actuator failure, so the root cause often lies in wiring, connectors, or module power supplies.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyProfessional

AreaComputer and output circuits

Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.