U0666

Lost Communication With Reductant Pressure Sensor

Moderate severity

The vehicle bus reports loss of communication with smart reductant (DEF/AdBlue) pressure sensor. Pump pressure feedback for the SCR dosing system is unavailable.

Common causes

Bus wiring open or shorted
One of the most commonly reported causes for this code — check this first.
high
Typical part cost: $220-1320
Module without power or ground
A plausible cause — test and verify before replacing parts.
medium
Typical part cost: $220-1320
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First things to check

1Confirm the code with a scan tool and check for additional related codes.
2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.

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Related codes

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Frequently asked questions

What does U0666 mean?

U0666 means "Lost Communication With Reductant Pressure Sensor". It is a generic OBD-II code that points to a fault in the network / communication.

What are the most common causes of U0666?

bus wiring open or shorted; module without power or ground; module failed — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.

Can I keep driving with this code?

The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical. Use the Wrenchify app for a full diagnosis specific to your vehicle.

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