U0657

Code

Generic U — Network/User

Lost Communication With Turbocharger/Supercharger Bypass Valve A Position Sensor

Brand: Generic

Type: U — Network/User

Views: UK: 17 EN: 25 RU: 15

AI status

Completed

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Page language: EN

Causes

Open or shorted wiring to the bypass valve A position sensor
Corroded or disconnected connector at the sensor or module
Failed turbo/supercharger bypass valve position sensor
Faulty turbocharger bypass actuator or internal connector
Loss of power or ground to the sensor circuit
CAN bus communication error or module fault

Symptoms

MIL/Check Engine lamp illuminated
Reduced engine performance or limp mode
Incorrect or no turbo boost control (overboost/underboost)
Hesitation, poor throttle response
Related drivability faults during boost control
Possible stored multiple communication or sensor codes

What to check

Read and record U0657 and any other stored DTCs and freeze frame data with a scan tool
Verify whether the code is current or intermittent; clear codes and attempt to re‑create
Visual inspection of bypass valve, sensor connector, and wiring for damage, corrosion, or water
Backprobe sensor connector to check for reference voltage, ground continuity, and signal voltage
Check fuse(s) and power feed to sensor circuit
Inspect CAN high/low lines for continuity and correct idle voltages; check for other modules reporting CAN errors

Signal parameters

Sensor reference voltage: typically 5.0 V (verify OEM spec)
Sensor ground: 0 V (check for low resistance to chassis ground)
Sensor signal: variable voltage proportional to valve position (often ~0.5–4.5 V) or specific CAN message payload
CAN bus idle voltages: CAN_H and CAN_L each ~2.5 V (verify differential waveforms with scope or CAN tool)
Expected message frequency: depends on OEM (position updates while valve moves or engine running)

Diagnostic algorithm

Verify and record the code with a scan tool; note freeze frame and related codes.
Clear the code and perform an operational test to see if the code returns and under what conditions.
Visually inspect sensor connector, pins, and harness for corrosion, bent pins, or damage. Repair as needed.
With harness access, backprobe and verify sensor reference voltage and ground with ignition on; compare to spec.
Measure sensor signal while operating the valve or commanding actuator (use live data or oscilloscope). Look for stable, varying waveform consistent with position changes.
If the sensor uses CAN messaging, check CAN_H and CAN_L for proper idle voltages and use a CAN logger to confirm the module is transmitting/receiving position messages.
Check continuity and resistance of signal/reference/ground wires between sensor and controlling module; repair any opens/shorts.
Wiggle test harness/connectors while monitoring for intermittent communication or signal dropouts; repair chafed sections or secure routing.
If wiring and supply are good but no signal, remove and bench-test or replace the bypass valve position sensor/actuator per OEM procedure.
If new sensor does not restore communication, suspect ECU/module fault; verify with replacement or bench testing and consult manufacturer technical information before replacing control module.
After repairs, clear codes and perform road/boost test to confirm proper operation and that the code does not return.

Likely causes

Damaged or disconnected sensor connector or pins
Broken/shorted signal or reference wire between sensor and ECU
Failed position sensor inside bypass valve actuator
Bad ground or fused power feed to sensor
CAN bus wiring short/low/high resistance causing message loss

Fault status

⚠️ Status

Lost communication with turbocharger/supercharger bypass valve A position sensor. The control module is not receiving valid position data or messages from the sensor circuit or CAN node; the fault may be caused by wiring, power/ground, sensor failure, or bus/module communication error.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours