A failed reductant level sensor or its internal electronics, which stops responding on the bus; Damaged, corroded, or disconnected wiring or connector pins at the sensor or at the module it reports to; A blown fuse or poor ground that supplies power to the reductant level sensor circuit; A shorted or open data bus wire between the sensor and the module, including chafed harness sections; A software or calibration issue in the control module that intermittently drops the sensor's messages; A faulty control module that has lost the ability to communicate on that particular bus segment; Low system voltage or a weak battery that causes modules to drop offline during cranking or heavy load

DTC codes / U06xx · Network communication / U0619

U0619Lost Communication With Reductant Level Sensor A

Q: What does code U0619 mean?

Lost Communication With Reductant Level Sensor A. U0619 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the reductant level sensor A, which is the sensor that reports how much diesel exhaust fluid (DEF) remains in the tank. The module that monitors the sensor, typically the engine control module or a dedicated aftertreatment controller, has stopped receiving valid data over the serial data bus for a calibrated amount of time.

U0619 is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the reductant level sensor A, which is the sensor that reports how much diesel exhaust fluid (DEF) remains in the tank. The module that monitors the sensor, typically the engine control module or a dedicated aftertreatment controller, has stopped receiving valid data over the serial data bus for a calibrated amount of time.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the check engine light or a dedicated service emissions system message
A driver information center warning showing the DEF level as unknown, blank, or stuck at a default value
No noticeable change in engine performance in many cases, especially if the fault is intermittent
Possible speed limitation or engine derate if the vehicle's strategy treats a lost DEF level signal as a critical emissions fault
Inability to clear the warning with a simple key cycle when the communication loss is hard
Other unrelated modules may show communication codes if the fault lies on a shared bus segment

Common causes, most likely first

A failed reductant level sensor or its internal electronics, which stops responding on the bus
Damaged, corroded, or disconnected wiring or connector pins at the sensor or at the module it reports to
A blown fuse or poor ground that supplies power to the reductant level sensor circuit
A shorted or open data bus wire between the sensor and the module, including chafed harness sections
A software or calibration issue in the control module that intermittently drops the sensor's messages
A faulty control module that has lost the ability to communicate on that particular bus segment
Low system voltage or a weak battery that causes modules to drop offline during cranking or heavy load

How to diagnose and fix it

Verify battery voltage and charging system output, then clear the code and test-drive to see if U0619 returns immediately or only under specific conditions
Inspect the reductant level sensor connector and the module connector for corrosion, pushed pins, or loose terminals, and check the sensor fuse and ground
Use a scan tool to view live data for reductant level and confirm whether the sensor value is present, frozen, or missing while other modules communicate normally
Perform a voltage drop and resistance check on the power, ground, and data bus wires between the sensor and the module it reports to
If the bus is healthy, substitute a known-good reductant level sensor or perform a module swap only after confirming the sensor is not responding
Check for technical service bulletins or calibration updates for the control module that address communication dropouts with the reductant level sensor
After repair, clear codes, perform any required DEF level relearn or adaptation, and verify the code does not reset through a complete drive cycle

Why the DEF level sensor goes silent

A reductant level sensor that reads empty or full incorrectly can still communicate perfectly, so U0619 is specifically about lost messages, not an inaccurate level reading.
Many technicians replace the sensor first, but a chafed data bus wire near the DEF tank or a corroded ground can mimic a failed sensor and cause the same communication loss.
On some vehicles the reductant level sensor shares a bus segment with other aftertreatment sensors, so a single shorted sensor can take down communication for several components and set multiple U-codes.
A weak battery or poor charging system can cause modules to drop offline momentarily during cranking, setting U0619 as a history code that never returns once the voltage issue is corrected.
The code can be stored by a module other than the engine controller, so always check which module reported U0619 before assuming the engine wiring is at fault.

Can I keep driving with U0619?

You can usually drive the vehicle short distances to a repair shop, but avoid long trips or heavy loads because a persistent reductant level communication fault can trigger an emissions-related derate or speed limitation. If the vehicle enters limp mode or shows a countdown to reduced power, stop driving and have it serviced immediately.

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.