P2BAD on GMC
NOx Exceedance - SCR Catalyst Conversion Efficiency
P2BAD on GMC vehicles indicates nox exceedance - scr catalyst conversion efficiency. Au7o has documented this code across 1 GMC model — most commonly on Sierra 3500HD. This code, found on modern diesels with selective catalytic reduction (SCR), means the system has detected that tailpipe NOx (nitrogen oxide) emissions have exceeded the legal limit because the SCR catalyst isn't converting them efficiently enough. The SCR system injects diesel exhaust fluid (DEF/AdBlue) over a catalyst to chemically break down NOx, and NOx sensors before and after the catalyst measure how well it's working. When the measured conversion falls below the required threshold, the computer flags this code, often triggering warning lights, a countdown to reduced power, or limp mode. Common roots are contaminated or low-quality DEF, a degraded catalyst, or faulty NOx sensors. Typical repair costs on GMC range from $300 to $2,000, depending on the specific model and root cause.
Common Causes of P2BAD
- •Contaminated, diluted, or low-quality diesel exhaust fluid (DEF)
- •Faulty NOx sensor (upstream or downstream)
- •Degraded, aged, or contaminated SCR catalyst
- •Faulty or clogged DEF/reductant injector
- •Insufficient DEF dosing or low DEF quantity
- •Exhaust leak before or within the SCR system
- •Faulty EGR system raising engine-out NOx
- •Wiring or connector faults to NOx sensors
P2BAD on GMC by Model
GMC Sierra 3500HD(1 issue)
- Diesel Exhaust Fluid (DEF) System Failures2011-2020
The Duramax diesel Sierra 3500HD (2011+) equipped with the DEF/SCR emission system develops failures in the DEF tank heater, DEF quality sensor, and associated wiring. Wires to the DEF tank short out, and because they share a harness with the transmission, this can trigger both DEF and transmission warnings simultaneously. Cold weather operation exacerbates DEF system problems as the fluid crystallizes.
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View P2BAD across all makes →Frequently Asked Questions
What does P2BAD mean on GMC?▼
P2BAD stands for "NOx Exceedance - SCR Catalyst Conversion Efficiency." This code, found on modern diesels with selective catalytic reduction (SCR), means the system has detected that tailpipe NOx (nitrogen oxide) emissions have exceeded the legal limit because the SCR catalyst isn't converting them efficiently enough. The SCR system injects diesel exhaust fluid (DEF/AdBlue) over a catalyst to chemically break down NOx, and NOx sensors before and after the catalyst measure how well it's working. When the measured conversion falls below the required threshold, the computer flags this code, often triggering warning lights, a countdown to reduced power, or limp mode. Common roots are contaminated or low-quality DEF, a degraded catalyst, or faulty NOx sensors. On GMC specifically, this code is documented across 1 model.
What causes P2BAD on GMC vehicles?▼
Common causes on GMC: Contaminated, diluted, or low-quality diesel exhaust fluid (DEF), Faulty NOx sensor (upstream or downstream), Degraded, aged, or contaminated SCR catalyst, Faulty or clogged DEF/reductant injector, Insufficient DEF dosing or low DEF quantity. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P2BAD on a GMC?▼
Repair costs on GMC range from $300 to $2,000, depending on the specific model and root cause.
Which GMC models have P2BAD documented?▼
Au7o has documented P2BAD on 1 GMC model: Sierra 3500HD.