DTC codes / P27xx · Transmission / P2778
P2778 indicates that the transmission control module (TCM) has detected an intermittent or erratic signal from the upshift switch circuit, which is part of the manual shift control system on automatic transmissions. The TCM expects a stable voltage or resistance from the switch when the driver requests an upshift, but the signal momentarily drops out or fluctuates, causing the TCM to set this code and potentially disable manual shift mode.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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