P0400: Exhaust Gas Recirculation (EGR) Flow Malfunction
5 vehicles · 5 makes · $75-$1,900 repair
Most Reported On
P0400 is an OBD-II diagnostic trouble code meaning “Exhaust Gas Recirculation (EGR) Flow Malfunction.” P0400 is a generic powertrain code indicating the engine computer detected a problem with exhaust gas recirculation (EGR) flow — either too much, too little, or incorrect flow compared to what was commanded. The EGR system routes a small amount of exhaust back into the intake to lower combustion temperatures and reduce emissions. A fault can cause rough idle, pinging/knock, increased emissions, and failed emissions testing, though it is generally not an immediate driving hazard. This code is most commonly reported on 1996-1997 Mazda MX-6, 2001-2010 Chrysler PT Cruiser, and 2007-2020 Mercedes-Benz Sprinter (OM642 3.0L V6, OM651 2.1L 4-cyl), plus 2 other vehicles, with repair costs ranging from $75 to $1,900.
Common Causes
Typical Repair Cost
Based on 5 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P0400, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Vehicles Affected (5)
FAQ
What does P0400 mean?
P0400 stands for "Exhaust Gas Recirculation (EGR) Flow Malfunction." P0400 is a generic powertrain code indicating the engine computer detected a problem with exhaust gas recirculation (EGR) flow — either too much, too little, or incorrect flow compared to what was commanded. The EGR system routes a small amount of exhaust back into the intake to lower combustion temperatures and reduce emissions. A fault can cause rough idle, pinging/knock, increased emissions, and failed emissions testing, though it is generally not an immediate driving hazard.
What are the most common causes of P0400?
The most common causes of P0400 are: Clogged or carbon-blocked EGR passages, Faulty EGR valve (stuck open or closed), Faulty EGR position or DPFE/flow sensor, Vacuum or electrical control fault to the EGR valve, Blocked or cracked EGR tube, Wiring/connector issues, PCM fault (rare). The specific cause varies by vehicle.
How much does it cost to fix P0400?
Repair costs for P0400 range from $75 to $1,900, depending on the vehicle and root cause.
Which vehicles are affected by P0400?
Au7o has documented P0400 across 5 vehicle models from 5 manufacturers: Chrysler, Mazda, Mercedes-Benz, Nissan, Toyota.
Sources (12)
- ForumHow to clean EGR valve? - Mazda MX-6 Forum
- ForumEGR Valve - symptoms? - Mazda MX-6 Forum
- ForumQ&A: Troubleshooting 1997 Mazda MX-6 Rough Idle and Acceleration Issues
- TSBTSB 19-001-08: EGR Valve Carbon Buildup on Chrysler PT Cruiser 2.4L Engine
- ForumPT Cruiser Forum Thread Discussing EGR Valve Failure and Carbon Buildup
- articleP0400 on 2007-2017 Mercedes-Benz Sprinter (OM642, OM651): EGR Flow Malfunction — Go-Parts
- articleP0401 on 2010-2018 Mercedes-Benz Sprinter 3.0L OM642: EGR Flow Insufficient — Go-Parts
- ForumP0401 EGR Insufficient Flow - Toyota Nation
- manufacturerInsufficient EGR Flow - P0401 Code - Toyota (Olathe Toyota Parts)
- ForumHelp with P0400 error code - Maxima.org 4th Gen
- articleP0400 Nissan: Meaning, Causes, Symptoms - Engine-Codes.com
- articleP0400 EGR Flow Malfunction diagnosis - Samarins
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.