Powertrain, generic (extended)

P21AB Reductant Level Sensor B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P21AB is the high-side counterpart: GM sets it when level sensor 2 shows an open load (between 3.56 and 4.74 V, read 1.5 ms after the test pulse) or a short to battery voltage (above 4.74 V), each for more than 3 s, as Type A on the 6.6L LML and the 2014 Cruze diesel. GM's preliminary bulletin PIP4887B for 2010–2011 Silverado, Sierra, Express and Savana with the LML or LGH engine names P21AB together with P203D and P21B0 and the message Service Exhaust Fluid System: inspect wiring, connectors and terminal tension also when the faults are merely stored, and replace the DEF tank only when the wiring is sound. For the 2011 model year GM sorted P21AB into its tamper-related group.

Likely causes

Open signal wire or spread terminal at the tank connector
Signal wire shorted to a voltage source
Level sensor B open inside the tank assembly

Symptoms

  • Check engine light on at once
  • Service Exhaust Fluid System message
  • Several level sensor codes stored together

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

P21A8P21AAP203DP21B0

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