U0656

Code

Generic U — Network/User

Lost Communication With Turbocharger/Supercharger Boost Control A Position Sensor

Brand: Generic

Type: U — Network/User

Views: UK: 16 EN: 29 RU: 17

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted wiring between sensor/actuator and control module
Disconnected, corroded or damaged connector pins
Failed boost control actuator or internal position sensor
Faulty PCM, turbo controller or a gateway module
Loss of reference power or ground to the sensor/actuator
Intermittent network (CAN/LIN) communications fault

Symptoms

Check Engine or MAL indicator illuminated
Reduced engine power, limp-home mode or derate
Abnormal boost control (overboost or underboost)
Hesitation, poor acceleration or turbo lag
Possible stored related boost or actuator DTCs
Fluctuating or no feedback on actuator position in scan tool

What to check

Read and record all stored DTCs and freeze frame data with a capable scan tool
Check for related codes (CAN bus, module comms, boost control faults)
Visually inspect connector and wiring to turbo actuator for damage, heat, corrosion or separation
Verify power and ground at the sensor/actuator connector (key-on and engine running where required)
Check reference signal (if used) such as 5V reference or sensor ground
Monitor live data for actuator position feedback and commanded position with a scan tool

Signal parameters

Position sensor type: potentiometer (0.5–4.5 V typical), Hall effect (0–5 V) or resolver (AC sine/cosine) depending on design
Expected idle/closed position voltage typically near one end of range (e.g., 0.5–1.0 V) and full travel near the other end (e.g., 4.0–4.5 V) — consult vehicle-specific data
Digital communication: CAN (watch for specific CAN ID frames carrying actuator status) or LIN for some actuator modules
If PWM position feedback used, expect a modulated duty cycle 0–100% corresponding to position
Supply voltage: typically 5 V reference; sensor ground should be near 0 V
Typical resistance values vary by design — check service data; open/infinite or short-to-ground/voltage indicates wiring/sensor fault

Diagnostic algorithm

Verify the concern: scan for DTC U0656 and any related codes. Note freeze frame and current engine conditions.
Inspect connectors and wiring at the turbo actuator/position sensor and at the PCM/module. Look for heat damage, crushed wires, corrosion, or pin backout.
With ignition on, backprobe the actuator connector: verify reference voltage (usually 5 V), sensor ground, and signal voltage. Compare to expected ranges.
If no power or ground, trace and repair fuse, relay, or fusible link supplying the circuit.
Monitor live data: command actuator to move (if supported by scan tool) and observe feedback. If commanded position changes but feedback does not, suspect sensor failure.
Perform continuity and resistance checks between actuator/sensor connector and PCM pins to find opens/shorts. Repair any damaged wiring.
Check CAN or LIN bus: measure bus voltages, check termination resistances, and verify other modules respond. Look for multiple modules reporting comms errors.
If wiring and bus are good, swap or bench-test the actuator/sensor where possible, or replace with a known-good unit.
After repair or replacement, clear codes and road-test. Re-scan for return of U0656 and verify proper boost control and actuator feedback.
If fault persists with good wiring and replacement actuator, escalate to module reflash, configuration check, or PCM/turbo controller replacement as per manufacturer guidance.

Likely causes

Damaged harness at flex points or near turbocharger heat-affected area
Contaminated or bent connector terminals at actuator or module
Failed actuator position sensor (internal potentiometer, Hall sensor or resolver)
Blown fuse or missing fuse supplying sensor/actuator power
Faulty local controller (turbo actuator module) or vehicle gateway

Fault status

⚠️ Status

Lost communication from Turbocharger/Supercharger Boost Control A position sensor/actuator. Control module not receiving expected position feedback or network messages.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours