Download Customer Concern: Tests/Procedures: Potential Causes: Check engine light is on for a code transmission P0715 (Input/Turbine Speed Sensor). 1. Scope the signal at the Powertrain Control Module (PCM) and watch for glitches while maneuvering the wire harness near the PCM connector. Wiring Reported Fix Details 2004 Mazda 3, 2.3L, USA/Canada * Input Speed Sensor – Car had a code p0715 and the a/t warning light was on. The transmission was downshifting on the freeway by itself. Replaced the input shaft speed sensor. Car is driving normally now, no trouble codes.