OBD-II code · Network
U0666 Lost Communication With Reductant Pressure Sensor
The vehicle bus reports loss of communication with smart reductant (DEF/AdBlue) pressure sensor. Pump pressure feedback for the SCR dosing system is unavailable.
Is it safe to drive with U0666?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyBus wiring open or shorted
- PossibleModule without power or ground
- PossibleModule 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
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Reductant Pressure Sensor, Vehicle Bus Wiring
Related codes
- U0663Lost Communication With Rear Mode Actuator
- U0664Lost Communication With Rear HVAC Air Cutoff Actuator
- U0665Lost Communication With Fuel Rail Pressure Sensor Bank 2
- U0667Lost Communication With Engine Oil Temperature Sensor A
- U0668Lost Communication With Engine Oil Level Sensor Circuit
- U0669Lost Communication With EGR Sensor D
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.