What does it mean?
P1771 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: TP Sensor Signal To TCM Circuit Malfunction (Open) .
Symptoms
- MIL (check engine lamp) is on and the transmission holds one gear in limp mode
- Shifts occur far too late or far too early because the module assumes a default load value
- No kickdown at all when the pedal is floored
- Harsh upshifts, as the module applies worst-case line pressure
- Cruise control refuses to set or drops out
- Hesitation and generally poor drivability
Likely causes
- Broken or corroded conductor in the throttle position signal wire running to the TCM (transmission control module)
- Backed-out, spread or pushed-in terminal at the TCM connector or at the sensor connector
- Throttle position sensor with an internally open resistive track, often at one end of its travel
- Missing 5 V reference or open sensor ground, which makes the signal look like an open circuit
- Damage from previous harness repairs, an aftermarket alarm or a stereo tapped into the shared signal wire
- Rodent damage or a chafed wire behind the engine where the harness passes the bulkhead
- Open input circuit inside the TCM
How to fix it
- Compare the throttle value reported by the engine module with the one the TCM reports; a large mismatch confirms the open
- Back-probe the throttle signal wire at the TCM while slowly sweeping the pedal and watch for the value dropping out
- Unplug both ends of the signal wire and check continuity end to end, then check it against ground
- Verify the 5 V reference and the ground at the sensor connector with the ignition on
- Wiggle the harness at the bulkhead and along the loom while watching live data to find an intermittent break
- Repair the open conductor or terminal; replace the sensor only if its own track is proven open, then relearn the throttle values