Powertrain, generic (extended)

P206B Reductant Quality Sensor Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P206B means the quality sensor answers, but its result cannot be used or does not fit what the SCR system does. GM sets it in its 2018 diesel table when the DEF controller keeps reporting the sensor as not ready, for instance because the ultrasonic echo is lost on a fouled sensor: 200 failed out of 250 samples, Type A, checked only with over 4 L of DEF and a sensor above 5 °C. GM bulletin 18-NA-124 for the 2018 Equinox and Terrain 1.6L diesel traces many cases to micro-bubbles from aerating filling equipment. Ford's 2023 diesels log an internal sensor error under P206B. Hino tests rationality: NOx conversion well below target while the sensor still claims usable fluid sets P206B with MIL. FCA lists it for its 3.0L diesels, and Ford SSM 51891 links it on 2023 Super Duty trucks with U02A2 and connector checks.

Likely causes

Air bubbles on the sensor after filling
Deposits or crystals on the ultrasonic sensor
Internal fault in the quality sensor or tank module
Drifting NOx sensor upsetting the rationality check (Hino logic)

Symptoms

  • MIL and Service Emission System or DEF message
  • Fault appears shortly or hours after refilling DEF
  • Possible countdown to speed limit

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant quality sensor

Related codes

P206AP206CP206DP207FP203B

References: gsi.ext.gm.com, static.nhtsa.gov, fordservicecontent.com, static.nhtsa.gov.