U061D

Code

Generic U — Network/User

Lost Communication With Reductant Temperature Sensor B

Brand: Generic

Type: U — Network/User

Views: UK: 28 EN: 39 RU: 25

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Page language: EN

Causes

Open or short in sensor B signal, supply, or ground circuit
Corroded/loose connector at the reductant temperature sensor B
Defective reductant temperature sensor B (thermistor or sender)
Faulty wiring harness (chafing, water intrusion, pinched)
Loss of sensor power/ground (fuse, relay, module output)
CAN/LIN network fault or module not reporting sensor data

Symptoms

DTC U061D stored or lamp/warning related to SCR/reductant system
Reduced or disabled reductant dosing (engine derate possible on some vehicles)
Unavailable reductant temperature B data in scan tool
Intermittent or no change in measured temperature for sensor B
Other network communication DTCs present (related modules)

What to check

Read and record all related DTCs and freeze frame data with a scan tool
Visually inspect the sensor B connector and wiring for damage, corrosion, or water
Backprobe sensor connector while monitoring live data — check for presence of reference voltage and ground
Check harness continuity and resistance between sensor connector and control module pins
Verify CAN/LIN bus health: measure bus idle voltages and termination resistance, check for related network codes
Compare readings from Reductant Temperature Sensor A and B (if present) for plausibility

Signal parameters

Sensor type: commonly an NTC thermistor (resistance varies with temperature) or voltage-output temperature sender
Expected output: resistance or voltage that changes smoothly with temperature (not open/short). Typical range covers ambient to high reductant temperatures (-40°C to +125°C) but values are vehicle-specific
Reference supply: often low-voltage reference (5V) or ground reference — verify with OEM data
Network: sensor data may be reported on a CAN or LIN message by a module; confirm presence of frames and that values update with temperature change
Electrical checks: continuity to module, no short to battery or ground, no excessive resistance in circuit

Diagnostic algorithm

Retrieve all codes and live data. Note whether only U061D is present or other network/sensor codes exist.
Perform visual inspection of sensor B connector and wiring. Look for bent pins, corrosion, water, or crushed wiring.
With ignition on (and engine off unless OEM directs otherwise), backprobe the sensor connector: verify reference voltage/pull-up, signal line behavior, and good ground. Record voltages.
If the sensor is a thermistor, measure resistance across sensor terminals at known temperatures (ambient and warmed) and confirm it changes. If voltage-output type, verify signal varies with temperature.
Check harness continuity between the sensor connector and the control module pin. Repair any opens or high-resistance connections.
Verify CAN/LIN bus operation: check idle voltages, termination (approx. 60 ohms across CAN_H and CAN_L), and use a scope or diagnostic tool to confirm messages containing reductant temperature B are present and updating.
Wiggle the wiring and connectors while watching live data to identify intermittent faults. Clean and reseal connectors if corrosion present.
If wiring and network are good but no proper signal, substitute a known-good sensor or connector assembly if available to confirm sensor failure before replacement.
After repairs, clear codes, perform a relearn or module initialization if required by OEM, then road test and re-scan to confirm U061D does not return.
If fault persists after sensor and wiring verification, consider module/software issues and consult OEM service information for module testing or reprogramming.

Likely causes

Connector corrosion or water ingress at the DEF temperature sensor
Broken/shorted wire in harness between sensor B and control module
Sensor B internal failure (open/short thermistor or failed electronics)
Loss of reference supply or ground to sensor circuit
CAN bus message from sensor's module not present or corrupted

Fault status

⚠️ Status

Lost Communication With Reductant Temperature Sensor B — the control module is not receiving valid sensor data or communication from the reductant temperature sensor designated B. Check wiring, connector, sensor, power/ground and the vehicle network.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours