P206D: Reductant Quality Sensor Circuit High

P206D is the upper limit counterpart of P206C. In GM's 2018 diesel table it is electrical: the piezo input of the ultrasonic quality sensor above 4.5 V in 40 of 50 samples, Type A. Ford's 2023 diesels set it when filtered urea concentration reads 60 % or more for over 900 s, which real DEF never reaches, so either the sensor or a foreign fluid is to blame. GM PIP5635 for 2019 Colorado and Canyon 2.8L names a false cause: urea crystals that form around the sensor when the fluid freezes and thaws. Before repairs, sensor status should read OK, concentration 28 to 40 % and the tank above 5 °C; if not, warm the truck indoors and drive it in traffic for 10 minutes. FCA STAR case S2025000006 for 2020 Wrangler and Gladiator diesels calls the code mainly electrical but asks for a refractometer and hydrocarbon strip test too.

Medium severity. Can I keep driving?Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

Symptoms

MIL and DEF or emission system warning
Fault often after cold nights
Countdown toward speed limit or no-restart

Most likely causes

Urea crystals around the sensor after freeze and thaw
Sensor signal open or shorted to voltage, failed sensor
Foreign or over-concentrated fluid in the tank

What to check, in order

Start with the simplest. You can tick off each step.

Check the AdBlue/DEF level and quality, and do not add additives or water
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Look for white crystals around the injector and the tank
Check connectors and heaters with the scanner
Run the dosing test available on your diagnostic tool
Replace parts only when the test points to that component

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P206D means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
6D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P206D?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P206D?

The most common causes are: urea crystals around the sensor after freeze and thaw; sensor signal open or shorted to voltage, failed sensor; foreign or over-concentrated fluid in the tank.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.