Transmission not shifting out of first gear, speedometer reads 0 mph. 2014 GMC Terrain. Innova SD35 Diagnostic Tablet LIVE CODE Reader shows zero MPH on Transmission output shaft.

Sounds like the output speed sensor has gone bad, or possibly a wiring issue.

This combination of symptoms on a 2014 GMC Terrain usually points more to a vehicle speed signal problem than an actual internal transmission failure.If the speedometer is stuck at 0 mph and your scan tool is also showing 0 from the transmission/output data, the TCM simply doesn’t know how fast the vehicle is moving. When that happens, it often defaults the transmission into a fail-safe mode and holds 1st gear.The most common causes are:Failed vehicle speed sensor (VSS) or output speed sensorDamaged wiring/harness between transmission and PCMABS wheel speed sensor issue (since some speed data is shared)Less commonly, a faulty PCM/TCM input