Powertrain, generic (extended)

P2BAA NOx Exceedence - Low Reagent Consumption

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

P2BAA means less reagent is actually reaching the exhaust than the dosing strategy asks for, so NOx stays too high. EU Annex XVI sets the frame: actual and demanded consumption are compared, and a gap above 50 % over 30 minutes triggers the warning. GM uses P2BAA on its diesel engines as Reductant Delivery Performance, Type A after one trip: 14OBDG04 checks a filtered DEF pressure drop against 365 kPa, while 16OBDG04 and 18OBDG04 compare the pressure drop after each injection with an expected value derived from pump duty. GM bulletin 25-NA-042 cures false P2BAA on 2023 Silverado 4500HD to 6500HD (L5D) with an ECM update. Neighbours: P2BA8 for stopped dosing, P2BA7 for an empty tank; drivers see a service emission system message.

Likely causes

Partially blocked DEF injector delivering too little

Weak DEF pump or clogged pump filter

Calibration error setting the code without a fault (GM 25-NA-042)

Leak in the pressure line returning fluid before the injector

Symptoms

Service emission or exhaust fluid system message
MIL on after one trip
DEF level falls more slowly than usual

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

scr systemreductant pumpreductant injection valve

Related codes

P249D P20E8 P2BA8 P2BA9 P208B

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