What Does P0C55 Mean?
This code indicates a general malfunction in the "A" position sensor circuit for drive motor "B" in a hybrid or electric vehicle. The powertrain control module has detected an electrical fault—such as an open, short, or signal outside expected parameters—in the resolver or rotary encoder that tracks motor "B" rotor position. Without accurate position data, the inverter cannot properly commutate the motor phases, leading to reduced power, torque shudder, or limp mode activation.
Safety Warning
Loss of accurate motor position data can cause unexpected torque surges, motor stalling, or complete loss of drive power. Vehicle may enter limp mode or become undriveable. Do not operate at highway speeds until resolved.
Common Causes
30%
Damaged or corroded position sensor connector or wiring harness
28%
Failed resolver or rotary position sensor in drive motor B
18%
Faulty hybrid/EV powertrain control module (inverter controller)
14%
Electromagnetic interference from high-voltage components affecting sensor signal
10%
Physical damage to sensor mounting or air gap misalignment
Diagnostic Steps
1
Retrieve freeze frame data and note vehicle speed, motor RPM, and battery state of charge at the time of the fault.
2
Inspect the wiring harness and connector for the motor B position sensor circuit A—check for corrosion, broken pins, chafed insulation, or moisture intrusion.
3
Measure resistance and continuity of the position sensor windings (excitation, sine, and cosine) against manufacturer specifications.
4
Use an oscilloscope to monitor the sensor output signals while slowly rotating the motor (if possible) to verify smooth, continuous waveform output.
5
Check the sensor mounting for physical damage, looseness, or debris that could affect the air gap between resolver rotor and stator.
6
If all wiring and sensor tests pass, suspect the inverter control module and perform manufacturer-specific diagnostics.
Estimated Repair Cost
$400 - $2,200
Parts + labor, varies by vehicle and location
This code indicates a general malfunction in the "A" position sensor circuit for drive motor "B" in a hybrid or electric vehicle. The powertrain control module has detected an electrical fault—such as an open, short, or signal outside expected parameters—in the resolver or rotary encoder that tracks...
The most common cause of P0C55 (Drive Motor "B" Position Sensor Circuit "A") is: Damaged or corroded position sensor connector or wiring harness
Typical repair costs for P0C55 range from $400 to $2,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of accurate motor position data can cause unexpected torque surges, motor stalling, or complete loss of drive power. Vehicle may enter limp mode or become undriveable. Do not operate at highway speeds until resolved.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0C55 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Drive Motor System
Difficulty
Type
Generic (SAE)
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