What Does P1777 Mean?
The transmission control module has detected an invalid signal from the driver mode selector switch (Performance/Normal/Winter modes). This switch allows the driver to change shift characteristics, and the TCM cannot properly interpret the input circuit.
Common Causes
35%
Faulty mode selector switch or button assembly
30%
Damaged or corroded wiring harness between switch and TCM
20%
Failed transmission control module (TCM)
15%
Poor electrical connection at switch or TCM connector
Diagnostic Steps
1
Step 1: Visually inspect the mode selector switch for physical damage or wear
2
Step 2: Test voltage at the switch connector with key on to verify power supply and ground
3
Step 3: Check resistance values of the switch in each mode position per manufacturer specifications
4
Step 4: Inspect wiring harness from switch to TCM for damage, chafing, or corrosion
5
Step 5: Monitor live data on scan tool while cycling through modes to identify signal dropout
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The transmission control module has detected an invalid signal from the driver mode selector switch (Performance/Normal/Winter modes). This switch allows the driver to change shift characteristics, and the TCM cannot properly interpret the input circuit.
The most common cause of P1777 (Performance / Normal / Winter Mode Input Malfunction) is: Faulty mode selector switch or button assembly
Typical repair costs for P1777 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains safe to drive but may not shift optimally for driving conditions. Performance or fuel economy may be slightly affected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1777 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Control System
Difficulty
Type
Manufacturer
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