Powertrain, generic (extended)

P21AE Reductant Level Sensor C Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P21AE stands for an implausible level sensor C signal whose voltage is still electrically valid. No manufacturer describes a separate check for this code in public material. GM shows how such plausibility testing can work: on the 2014 Cruze diesel the ECM compares the readings of all three discrete level sensors after the test pulse and flags combinations that cannot physically occur together, but files the result under P203B rather than under a code for the sensor concerned. For the 2018 Cruze, GM did assign P21A9 to sensor 2. A maker using P21AE would point to sensor C itself, for instance after urea crystal deposits or partial freezing. Electrical faults of this sensor are covered by P21AF and P21B0.

Likely causes

Crystallised urea on level sensor C
Partly frozen fluid around the sensor
Level sensor C drifting or degraded

Symptoms

  • Check engine light on
  • DEF level display does not match the refill amount
  • Possible DEF warning sequence

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,200
Time0.5–4 h

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

Parts involved

reductant level sensor

Related codes

P21ADP21AFP21B0P21A9P203B

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.