OBD-II code P2777 indicates that the transmission control module (TCM) or powertrain control module (PCM) has detected an abnormally high voltage signal in the upshift switch circuit. This typically means the switch or its wiring is shorted to power or the switch is stuck in the 'on' position.
The switch itself may be internally shorted or mechanically stuck, causing a constant high-voltage signal to the TCM/PCM.
Chafed, pinched, or frayed wires between the switch and the TCM/PCM can short to power, creating a high-voltage signal.
Poor connections at the switch, TCM/PCM, or along the wiring harness can cause intermittent or persistent high-voltage readings.
While rare, a malfunctioning TCM or PCM could misinterpret the switch signal or have an internal short, though this is uncommon for P2777.
You may be able to drive, but the transmission may not shift properly, potentially causing poor fuel economy, reduced performance, or further damage. Address the issue promptly.
No. While a faulty TCM or PCM *can* cause this code, it is very rare. The issue is almost always the upshift switch, wiring, or connectors. Replace the TCM/PCM only after thorough testing confirms it is the root cause.
Disconnect the switch and use a multimeter to check for resistance or continuity in both switch positions. Compare your readings to the manufacturer’s specifications. If the switch fails these tests, it should be replaced.
Software issues are unlikely to cause P2777, as this code relates to a physical electrical signal. However, if all other components test normal, a TCM/PCM software update or reflash may be recommended by the manufacturer.