U0619: Lost Communication With Reductant Level Sensor A

What it means

The vehicle bus reports loss of communication with smart reductant (DEF/AdBlue) level sensor A. Tank-level monitoring switches to a substitute model; refill warnings may be incorrect.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

Reductant level sensor A monitors the DEF or AdBlue tank and sends level information over the vehicle communication bus. U0619 sets when the control module stops receiving messages from sensor A, so tank-level monitoring may use an estimate and refill warnings may be inaccurate.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Record freeze-frame data and scan all modules for communication faults to see whether sensor A alone has dropped offline.
2. Compare live reductant level data with the actual tank level, noting whether sensor A's reading is missing or unavailable.
3. Inspect sensor A's connector and bus wiring near the reductant tank for corrosion, fluid contamination, loose terminals, or physical damage.
4. Check power and ground at the sensor A module using the manufacturer's wiring information.
5. Test the sensor communication circuit for opens or shorts following the manufacturer's procedure, and repair any wiring fault.
6. If wiring and supply connections are sound, verify sensor A communication before replacing the sensor module.

Common fixes

• Reconnect and secure the reductant level sensor A connector.
• Clean corrosion or repair damaged terminals at sensor A's connector.
• Repair damaged, open, or shorted communication wiring to sensor A.
• Restore the sensor module's power or ground connection.
• Replace reductant level sensor A if it fails communication testing with a verified circuit.

Can I keep driving?

The vehicle may remain drivable if it runs normally, but check the actual DEF or AdBlue level and avoid long trips until the fault is diagnosed because the displayed level and refill warnings may be wrong. Emissions-system warnings or operating restrictions may follow if the tank runs low.