P229F on Mercedes-Benz
NOx Sensor Circuit Range/Performance (Bank 1 Sensor 2)
P229F on Mercedes-Benz vehicles indicates nox sensor circuit range/performance (bank 1 sensor 2). Au7o has documented this code across 4 Mercedes-Benz models — most commonly on GLA, GLE, Sprinter. P229F indicates the engine control module detected a range/performance problem with the downstream NOx sensor on bank 1 (sensor 2), most common on diesel vehicles with SCR/AdBlue emissions systems. The NOx sensor measures nitrogen-oxide levels in the exhaust so the system can dose diesel exhaust fluid correctly and verify the catalyst is working. An implausible or out-of-range signal can trigger emissions warnings, reduced power, and on many diesels eventual no-start countdowns tied to emissions compliance. It is an emissions-system fault that should be addressed before it escalates. Typical repair costs on Mercedes-Benz range from $300 to $3,500, depending on the specific model and root cause.
Common Causes of P229F
- •Faulty downstream NOx sensor (bank 1 sensor 2)
- •Wiring or connector corrosion at the NOx sensor
- •Exhaust leak upstream of the sensor
- •Contaminated or incorrect diesel exhaust fluid (DEF/AdBlue)
- •SCR catalyst degradation
- •NOx sensor control-module communication fault
- •ECM software needing update/recalibration
P229F on Mercedes-Benz by Model
Mercedes-Benz GLA(1 issue)
- Diesel EGR/DPF Clogging & AdBlue (SCR) System Faults (OM651/OM654)2015-2023
GLA diesels (GLA 200d/220d), popular in Germany and the EU, develop clogged EGR valves and diesel particulate filters from soot buildup, plus AdBlue/SCR (NOx reduction) faults. EGR carbon fouling causes rough idle, reduced power and emissions faults; DPF blockage triggers limp mode if regeneration can't complete (common with short urban trips). AdBlue/SCR issues include crystallization from irregular use, sensor/NOx-sensor faults, level/quality warnings and countdown-to-no-start messages. The OM651 also shares timing-chain-stretch tendencies.
Mercedes-Benz GLE(1 issue)
- Diesel AdBlue / SCR NOx Sensor Fault Triggering Restart Countdown and No-Start2016-2024
On diesel GLEs, the SCR/AdBlue emissions system enforces compliance with a start countdown: when it detects a fault it warns 'You can restart the engine X more times,' and once the counter expires the car will not start until the fault is fixed and the counter is reset. The most common root cause is a failed upstream or downstream NOx sensor giving out-of-range readings; other causes are AdBlue crystallization, a blocked dosing valve, or low-quality fluid. Topping up AdBlue does NOT clear the countdown.
Mercedes-Benz Sprinter(1 issue)
- DEF/AdBlue SCR System Faults and Derate2014-2025
The Sprinter diesel exhaust fluid (DEF/AdBlue) selective catalytic reduction system is plagued by faults in the dosing module, NOx sensors, DEF heater, and SCR catalyst. Failures trigger the dreaded "engine derate" countdown that limits vehicle speed to 5 mph if not resolved, stranding commercial vehicles. The system is sensitive to DEF quality and cold weather.
Mercedes-Benz V-Class(1 issue)
- AdBlue/SCR System Faults Triggering Limp Mode and No-Start Countdown2015-2020
On Euro 6 W447 diesels the SCR emissions system depends on NOx sensors (before and after the catalyst) and the AdBlue dosing system. A failed NOx sensor, dosing fault, or low/contaminated AdBlue escalates from a yellow warning to a red warning and finally a 'No start in X miles' countdown, after which the engine will not restart once switched off. The vehicle commonly drops into limp mode (restricted speed/power) before that. NOx sensor failure is one of the most frequently cited W447 emissions faults.
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View P229F across all makes →Frequently Asked Questions
What does P229F mean on Mercedes-Benz?▼
P229F stands for "NOx Sensor Circuit Range/Performance (Bank 1 Sensor 2)." P229F indicates the engine control module detected a range/performance problem with the downstream NOx sensor on bank 1 (sensor 2), most common on diesel vehicles with SCR/AdBlue emissions systems. The NOx sensor measures nitrogen-oxide levels in the exhaust so the system can dose diesel exhaust fluid correctly and verify the catalyst is working. An implausible or out-of-range signal can trigger emissions warnings, reduced power, and on many diesels eventual no-start countdowns tied to emissions compliance. It is an emissions-system fault that should be addressed before it escalates. On Mercedes-Benz specifically, this code is documented across 4 models.
What causes P229F on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Faulty downstream NOx sensor (bank 1 sensor 2), Wiring or connector corrosion at the NOx sensor, Exhaust leak upstream of the sensor, Contaminated or incorrect diesel exhaust fluid (DEF/AdBlue), SCR catalyst degradation. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P229F on a Mercedes-Benz?▼
Repair costs on Mercedes-Benz range from $300 to $3,500, depending on the specific model and root cause.
Which Mercedes-Benz models have P229F documented?▼
Au7o has documented P229F on 4 Mercedes-Benz models: GLA, GLE, Sprinter, V-Class.