U0655

Code

Generic U — Network/User

Lost Communication With Diesel Intake Air Flow B Position Sensor

Brand: Generic

Type: U — Network/User

Views: UK: 24 EN: 39 RU: 22

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, shorted, or intermittent wiring between sensor and control module (CAN/LIN or dedicated signal wires)
Corroded, loose, or damaged connector(s) at the sensor or module
Sensor (intake air flow / flap position sensor B) internal failure
Loss of sensor supply (5 V reference) or ground
CAN/LIN bus fault: missing termination, short to battery/ground, or high bus error rate
Blown fuse or power distribution issue feeding the sensor or module

Symptoms

Stored U0655 (communication lost with Intake Air Flow B Position Sensor)
Check Engine Light (MIL) or warning indicator set in some vehicles
Reduced engine performance, limp-home behavior, or restricted turbo/air control
Irregular intake flap/metering behavior, possible rough idle or poor throttle response
Related system warnings (emissions, regeneration, or reduced power)

What to check

Read all stored/active freeze frame data and related codes with a scan tool; note occurrence conditions
Check for other network-related U-codes (CAN/LIN) or multiple sensor communication faults
Visually inspect sensor B connector and wiring for corrosion, damage, pin push-out, or moisture
Verify fuses and power distribution feeding the sensor and related modules
Measure sensor supply (reference) voltage and ground at the connector with key on (per vehicle spec)
Use scope to view CAN_H/CAN_L or LIN waveform and check for normal recessive/dominant levels and packet activity

Signal parameters

CAN bus recessive voltage: about 2.5 V on CAN_H and CAN_L (differential ~0 V); dominant state typically CAN_H ~3.5 V and CAN_L ~1.5 V (differential ≈ 2 V)
LIN bus idle: pull-up to system supply (varies by manufacturer) and single-wire packet pulses (use scope to confirm activity)
Typical sensor position signal (if analog potentiometer): ~0.5–4.5 V output range referenced to sensor ground
Sensor supply/reference: typically 5 V reference (verify vehicle-specific value)
Expected continuity/impedance: CAN pair ~60 ohm across termination (two 120 ohm in parallel) when powered; check wiring harness resistance for opens/shorts

Diagnostic algorithm

Retrieve DTC(s) and live data; record freeze frame and note whether code is intermittent or permanent.
Inspect sensor B connector, pins, and harness for moisture, corrosion, bent pins or damage; repair as needed.
Verify power and ground at the sensor connector with key ON (measure battery voltage on power pin, and low resistance to chassis on ground).
Check the sensor reference voltage (typically 5 V) and the sensor output signal while moving the intake flap (if applicable).
Monitor network traffic for the sensor using a capable scan tool or oscilloscope; confirm CAN_H/CAN_L differential waveforms and packet activity when fault is active.
Perform a continuity test between sensor connector and control module connector to find opens/shorts; check for short to battery or ground.
Wiggle the harness and connectors while monitoring for intermittent loss of communication; repair damaged wiring or connector lock issues.
If wiring and power/ground are correct but no sensor communication, swap or bench-test the sensor (if serviceable) or replace the sensor and retest.
If problem persists after sensor and wiring verification, suspect the control module or bus termination; inspect CAN termination resistors and other modules on the same bus.
Clear codes and road-test to verify repair. Check for required module reprogramming or software updates/TSBs if fault recurs.

Likely causes

Damaged/loose connector at the intake air flow position sensor
Broken or chafed wiring harness to sensor B (open or intermittent)
Failed sensor electronics (internal communication driver)
Loss of 5 V reference or ground at the sensor
CAN bus wiring short or missing termination resistor

Fault status

⚠️ Status

Lost communication with Diesel Intake Air Flow B Position Sensor — no valid messages or expected signal received from sensor B. May cause degraded intake control and driveability warnings.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours