Damaged, chafed, or corroded wiring in the sensor harness or connector, especially near the exhaust and underbody where heat and road debris attack insulation; Failed particulate matter sensor B itself, either an internal electronics failure or a sensing element contaminated by excessive soot or ash; Poor electrical connection at the sensor plug or at the control module, including backed-out terminals or water intrusion; Blown fuse or damaged relay supplying power to the sensor circuit; CAN bus communication fault such as a shorted or open data line between the sensor and the module, or a faulty terminating resistor elsewhere on the network; Software or calibration issue in the control module that intermittently drops the sensor from the network; Low battery voltage or charging system fault that causes modules to reset and lose communication during cranking or heavy electrical load

DTC codes / U01xx · Lost communication with a control module / U01B1

U01B1Lost Communication With Particulate Matter Sensor B

Q: What does code U01B1 mean?

Lost Communication With Particulate Matter Sensor B. U01B1 is a generic network communication code indicating that a control module on the vehicle's controller area network (CAN) bus has lost contact with the particulate matter sensor labeled B, which is typically the downstream sensor on a dual-sensor exhaust aftertreatment system. The module monitoring this sensor has stopped receiving valid messages from it for a calibrated period, so it sets this code and usually illuminates the malfunction indicator lamp.

U01B1 is a generic network communication code indicating that a control module on the vehicle's controller area network (CAN) bus has lost contact with the particulate matter sensor labeled B, which is typically the downstream sensor on a dual-sensor exhaust aftertreatment system. The module monitoring this sensor has stopped receiving valid messages from it for a calibrated period, so it sets this code and usually illuminates the malfunction indicator lamp.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

Malfunction indicator lamp (MIL) illuminated, often with no other noticeable symptoms
Reduced engine power or limp mode on some vehicles when the sensor is part of emissions compliance logic
A message on the driver information display indicating an emissions system or sensor fault
Slightly increased fuel consumption if the engine management strategy defaults to a less efficient particulate filter regeneration schedule
Intermittent warning light that comes and goes with vibration, moisture, or temperature changes
Possible stored freeze-frame data showing the fault occurred during a regeneration or at a specific battery voltage

Common causes, most likely first

Damaged, chafed, or corroded wiring in the sensor harness or connector, especially near the exhaust and underbody where heat and road debris attack insulation
Failed particulate matter sensor B itself, either an internal electronics failure or a sensing element contaminated by excessive soot or ash
Poor electrical connection at the sensor plug or at the control module, including backed-out terminals or water intrusion
Blown fuse or damaged relay supplying power to the sensor circuit
CAN bus communication fault such as a shorted or open data line between the sensor and the module, or a faulty terminating resistor elsewhere on the network
Software or calibration issue in the control module that intermittently drops the sensor from the network
Low battery voltage or charging system fault that causes modules to reset and lose communication during cranking or heavy electrical load

How to diagnose and fix it

Perform a full scan of all modules and record all stored, pending, and permanent codes to see whether U01B1 is isolated or part of a broader network problem
Inspect the particulate matter sensor B harness and connector for chafing, heat damage, corrosion, and tight terminal fit, repairing any damaged wire or pin as needed
Check the sensor supply fuse and verify battery voltage and charging system output, since low voltage can trigger communication codes
Measure CAN bus resistance and voltage at the sensor connector or module to confirm the data lines are intact and not shorted or open
If wiring and power are good, substitute a known-good particulate matter sensor B and clear codes to see whether communication returns
Check for technical service bulletins or calibration updates for the control module that address intermittent sensor communication loss
After repair, clear all codes, perform any required adaptation or relearn procedure, and complete a drive cycle that includes a regeneration event to verify the fix

Communication codes are not always sensor failures

A U01B1 code frequently appears after a low-voltage event such as a weak battery or a jump start, and the sensor itself is fine once the charging system is repaired and codes are cleared.
Technicians often replace the particulate matter sensor B only to find the real fault is a chafed wire in the harness near the exhaust hanger or a corroded connector pin that was disturbed during the repair.
This code can be set by a fault in another module on the same CAN bus that disrupts network traffic, so a full network scan is more valuable than focusing only on the sensor circuit.
On some vehicles the particulate matter sensor communicates on a dedicated sub-bus, and a single failed sensor can take down communication for other components on that segment, producing multiple U-codes that look unrelated.
Clearing the code without repairing the underlying intermittent connection often results in the code returning weeks later, usually when the vehicle is driven in wet or cold conditions that affect the damaged circuit.

Can I keep driving with U01B1?

The vehicle is generally safe to drive short distances because the fault is a communication loss rather than a mechanical failure, but avoid long trips, heavy loads, or towing until it is repaired. Prolonged driving with this code can prevent particulate filter regeneration and lead to a clogged filter or reduced engine power, so schedule diagnosis promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.