Powertrain, generic (extended)

P21AD Reductant Level Sensor C Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P21AD covers the electrical circuit of the third reductant level sensor, so it only exists on tanks with at least three level points. GM's 6.6L Duramax and 2014 Cruze diesel are such cases: the tank electronics test sensors 1 to 3 separately and pass each status to the ECM over CAN. GM uses the specific codes P21AF and P21B0 instead of this summary code. If P21AD shows up together with P21A8 and P203A, a shared supply, ground or the tank connector is far more likely than three failed sensors at once. Since the level information feeds the DEF range and refill warnings, drivers may see a missing or wrong range message besides the MIL. CARB asks for circuit monitoring of such inputs in 13 CCR 1968.2 (f)(15.2.1).

Likely causes

Fault in a supply, ground or connector shared by the level sensors
Level sensor C in the tank assembly failed
Sensor C signal wire damaged

Symptoms

  • Check engine light on
  • DEF range message missing or implausible
  • Further level sensor codes stored

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,200
Time0.5–4 h

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

Parts involved

reductant level sensor

Related codes

P21AEP21AFP21B0P21B1P21A8P203A

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