U01B1

Code

Generic U — Network/User

Lost Communication With Particulate Matter Sensor B

Brand: Generic

Type: U — Network/User

Views: UK: 47 EN: 58 RU: 30

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Page language: EN

Causes

Faulty particulate matter sensor B (internal failure)
Open, short or intermittent wiring between sensor B and control module
Corroded or loose connector(s) at the sensor or control module
Faulty CAN/LIN bus, missing termination, or bus wiring damage
Blown fuse or lost power/ground to the sensor circuit
Water intrusion or physical damage to sensor harness or connector

Symptoms

MIL/Check Engine lamp or DPF warning illuminated
DPF regeneration inhibited or forced regen commands, reduced aftertreatment performance messages
Reduced engine power or limp mode in some systems
Diagnostic trouble code U01B1 stored (lost communication)
In some vehicles, related ABS/traction/engine functions may show reduced diagnostics

What to check

Use a scan tool and read all stored U-codes and freeze frame data; note whether sensor B telemetry is present
Check for other communication-related codes (other modules showing lost communications)
Visually inspect particulate matter sensor B, connector, and harness for damage, corrosion, water, or contamination
With key on engine off, measure reference power and ground at the sensor connector per wiring diagram
Verify communication bus state at the sensor connector: presence of CAN/LIN signals and expected idle voltages
Check fuses and module power supplies that feed the sensor or communication gateway

Signal parameters

CAN bus recessive voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both); dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
Typical CAN data rates: commonly 250 kb/s or 500 kb/s (verify vehicle specific)
LIN bus idle ≈ battery voltage; LIN dominant pulls low (if sensor B uses LIN, check according to manufacturer)
Sensor supply voltage: vehicle battery voltage (check for ~12 V with key on)
Sensor ground: near 0 V (low resistance to chassis ground)

Diagnostic algorithm

Connect a full-function scan tool and verify U01B1 and any related codes; record freeze frame and live data, then clear codes to see if they return
Confirm whether PM Sensor A (if present) communicates correctly to isolate bus vs sensor-specific issue
Inspect the sensor B connector and harness for corrosion, bent pins, burning, or water intrusion. Repair or replace damaged connectors
Check power and ground at the sensor with key on (voltage at supply pin, continuity to chassis ground). Repair any open circuits or poor grounds
Backprobe the communication lines at the sensor connector and observe waveform/voltages with an oscilloscope or data logger while the system is active. Look for normal idle voltages and message activity
If bus appears dead at the sensor, trace wiring toward the nearest module/gateway. Check continuity and resistance between sensor connector and control module pins; repair shorts/opens
Verify termination resistors on the CAN bus (two 120 ohm in parallel ≈60 ohm across CAN_H and CAN_L). Replace or repair termination if incorrect
If wiring and power/ground are good but no communication, swap or substitute with a known good PM sensor B (if possible) or swap sensors A/B if identical and supported, then observe if the code follows the sensor
If swapping does not move the fault, investigate control module or gateway software/firmware and consult manufacturer service information/TSBs; reprogram or replace module only after confirming harness/sensor failure
After repairs, erase codes and perform a road/regen cycle or use guided tests to confirm normal operation and that U01B1 does not return