This code indicates the engine control module (ECM) has lost digital communication with the secondary (or 'B') intake air flow position sensor on a diesel engine, typically via the CAN or LIN data bus. The loss of signal prevents the ECM from monitoring intake air mass or throttle flap position, often triggering reduced power mode to protect the engine.
Corroded, damaged, or loose terminals in the sensor harness or connector interrupt the communication lines or power and ground circuits, which is the most common root cause for U-codes.
The air flow position sensor’s internal communication circuitry has failed, preventing it from responding to bus requests despite receiving correct power and ground.
A blown fuse, corroded ground eyelet, or high-resistance connection on the sensor’s reference voltage circuit causes intermittent or total communication loss.
An open circuit, short-to-power, or short-to-ground in the CAN high/low or LIN bus lines connecting the sensor to the network disrupts data transmission.
Rare internal ECM hardware fault affecting the specific communication circuit for this sensor; verify all wiring, power, and sensor integrity before considering this possibility.
No. Communication loss is more frequently caused by wiring, connector corrosion, or power supply issues than by the sensor itself; always inspect the harness and terminals first.
Driving is not recommended. Diesel engines rely on accurate air flow data for emissions control and fuel metering; the vehicle will likely enter limp mode with significantly reduced power and potential catalyst damage risk.
Probably not. While a failed ECM can theoretically cause this code, it is statistically unlikely. Exhaust all wiring, connector, and sensor testing before considering control module replacement, as misdiagnosis leading to unnecessary ECM replacement is common.
It typically denotes a secondary sensor in a dual-sensor assembly, the sensor on bank B of a V-configuration engine, or the second redundant sensor in the intake tract; consult the specific service manual for your engine configuration to confirm.