Powertrain, generic (extended)

P2BAD NOx Exceedence - Root Cause Unknown

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P2BAD is the catch-all of the series: NOx after the SCR is measured too high, yet none of the specific causes from P2BA6 to P2BAC can be pinned down. GM uses it on the 2014 Duramax 6.6 L LML as Exhaust NOx Concentration High - Unknown Reason: the measured SCR efficiency, minus an offset-corrected model value, is filtered over time and fails once the difference drops below zero, with both NOx sensors active for over 60 s; Type A. GM PIP5007 notes that from 2012 this code takes over from P20EE/P207F as the diagnostic path when the DIC reports poor fluid quality. Nissan lists it as NOx Concentration Exceeded for the 2016 Titan XD with the Cummins 5.0 L and fixes it by reflashing the ECM. Diagnosis starts with DEF quality, dosing and sensors.

Likely causes

Poor DEF quality or partly blocked dosing without a specific code
Aged or deposit-covered SCR catalyst
Upstream or downstream NOx sensor drifting
Engine control software needing an update (Nissan Titan XD)

Symptoms

  • Exhaust fluid quality poor or emission warning
  • MIL on after the first failed run
  • Speed limit countdown if the condition persists

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–3,000
Time1–6 h

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

Parts involved

scr systemnox sensor

Related codes

P20EEP207FP2BA6P2BAE

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