P2BAD on Peugeot: How to Diagnose & Fix

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 Peugeot it is documented across 2 models: 308, 3008.

The most common causes of P2BAD are: 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. The specific cause varies by vehicle.

Published repair estimates on Peugeot range from $300 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.