P0401 on Mercedes-Benz
Exhaust Gas Recirculation Flow Insufficient
P0401 on Mercedes-Benz vehicles indicates exhaust gas recirculation flow insufficient. Au7o has documented this code across 4 Mercedes-Benz models — most commonly on B-Class, GLA, GLS. This code means the Exhaust Gas Recirculation (EGR) system is not flowing enough exhaust back into the engine. The EGR system recirculates a small amount of exhaust into the intake to lower combustion temperatures and reduce nitrogen oxide (NOx) emissions; the computer has determined the actual flow is below what it commanded. The most common reason is carbon buildup clogging the EGR valve or its passages. You may notice pinging/knocking, rough idle, or a check engine light, and the car will fail emissions testing. Typical repair costs on Mercedes-Benz range from $200 to $2,500, depending on the specific model and root cause.
Common Causes of P0401
- •Carbon buildup clogging the EGR valve or passages
- •Stuck or faulty EGR valve
- •Blocked or restricted EGR ports/tubes
- •Faulty EGR temperature or position sensor
- •Faulty DPFE/EGR pressure sensor (on applicable systems)
- •Vacuum leak or failed vacuum control (vacuum-operated EGR)
- •Wiring or connector problems at the EGR valve
P0401 on Mercedes-Benz by Model
Mercedes-Benz B-Class(1 issue)
- OM651 Diesel DPF and EGR Clogging (B180 CDI / B200 CDI)2013-2019
The 2.2L OM651 diesel in B180 CDI / B200 CDI variants is prone to diesel particulate filter (DPF) blockage and EGR-valve carbon fouling, especially on short urban trips where the exhaust never reaches regeneration temperature. Symptoms include reduced power (limp mode), increased fuel consumption, frequent failed regenerations, and warning lights. Carbon buildup in the EGR valve and intake also causes hesitation and rough running. The OM651 timing chain can also stretch and rattle, compounding diesel reliability concerns.
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 GLS(1 issue)
- OM656 Diesel Emissions System Clogging (EGR/DPF/AdBlue SCR) and Limp Mode2020-2025
EU-market GLS 350d/400d models with the OM656 3.0L inline-six diesel suffer from sensitivity in the exhaust aftertreatment chain. The EGR (AGR) valve, diesel particulate filter (DPF) and SCR/AdBlue system are sensitive to poor fuel quality, short-trip driving and temperature swings. Clogged DPF, a dirty/sticking EGR valve, or a faulty EGR differential-pressure sensor cause power loss, failed regenerations, dashboard warnings and limp-home mode. A German motor-talk owner thread on the GLS X167 400d documents poor acceleration that resolves after a restart, traced to a replaced EGR differential-pressure sensor under warranty. This primarily affects diesels not sold in the US, so it is especially relevant to the EU market.
Mercedes-Benz Sprinter(1 issue)
- EGR Valve and EGR Cooler Carbon Clogging (Limp Mode, P0400-Series Codes)2007-2020
Sprinter diesels (OM642 V6 and OM651 4-cylinder) recirculate soot-laden exhaust through the EGR valve and cooler. Over tens of thousands of miles the valve and the cooler's small passages choke with hard carbon, causing the valve to stick, EGR flow to read out of range, rough running, power loss and limp mode. Short-trip/urban duty cycles accelerate the buildup. The cooler is often more clogged than the valve and frequently cannot be cleaned, requiring replacement.
Looking for P0401 on a different make?
View P0401 across all makes →Frequently Asked Questions
What does P0401 mean on Mercedes-Benz?▼
P0401 stands for "Exhaust Gas Recirculation Flow Insufficient." This code means the Exhaust Gas Recirculation (EGR) system is not flowing enough exhaust back into the engine. The EGR system recirculates a small amount of exhaust into the intake to lower combustion temperatures and reduce nitrogen oxide (NOx) emissions; the computer has determined the actual flow is below what it commanded. The most common reason is carbon buildup clogging the EGR valve or its passages. You may notice pinging/knocking, rough idle, or a check engine light, and the car will fail emissions testing. On Mercedes-Benz specifically, this code is documented across 4 models.
What causes P0401 on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Carbon buildup clogging the EGR valve or passages, Stuck or faulty EGR valve, Blocked or restricted EGR ports/tubes, Faulty EGR temperature or position sensor, Faulty DPFE/EGR pressure sensor (on applicable systems). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0401 on a Mercedes-Benz?▼
Repair costs on Mercedes-Benz range from $200 to $2,500, depending on the specific model and root cause.
Which Mercedes-Benz models have P0401 documented?▼
Au7o has documented P0401 on 4 Mercedes-Benz models: B-Class, GLA, GLS, Sprinter.