What it means
The reductant tank B temperature sensor signal drops out or jumps intermittently. Loose connector or noisy ground.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The reductant tank B temperature sensor supplies tank temperature information to the emissions control module for DEF system operation. This code sets when the sensor signal jumps or drops out intermittently, often because the connector or ground reference loses a stable connection, particularly with vibration.
Common causes
Most likely first.
- Sensor connector not seated
- Noisy ground reference
- Connector with intermittent contact under vibration
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Save freeze-frame data and review live tank B temperature while the fault is present, looking for sudden jumps or dropouts.
- Inspect the tank B sensor connector for incomplete seating, corrosion, loose terminals, or pins that move in the connector body.
- Examine the harness and ground reference for chafing, loose connections, or damage, and check whether movement of the harness coincides with an unstable reading.
- Use the wiring diagram to test continuity and ground stability while gently flexing the relevant harness sections.
- If wiring and connections are sound, test the tank B sensor against the manufacturer's specification and replace it only if it drops out.
Common fixes
- Seat and secure the tank B sensor connector.
- Clean corroded terminals and repair loose or damaged connector pins.
- Repair a damaged ground or harness section causing an unstable reference.
- Replace the tank B temperature sensor if it fails an intermittent fault test.
- Clear the code and verify that the live reading stays stable during operation.
Can I keep driving?
You may be able to drive briefly if the vehicle runs normally, but an unstable DEF temperature signal can trigger emissions warnings or a no-start countdown. Avoid long trips and address it promptly if a countdown or reduced-power warning appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.