P0400 on Nissan: How to Diagnose & Fix
Exhaust Gas Recirculation (EGR) Flow Malfunction
1 Nissan model · 1 documented issue · $80-$300 repair
P0400 on Nissan by model: symptoms, diagnosis and fix
Nearly every high-mileage 4th-gen Maxima eventually sets a P0400 (EGR flow insufficient) code. The root cause is almost never the EGR valve itself; instead the small EGR pipe and the port where the EGR temperature sensor sits pack with carbon, so exhaust gas can no longer flow past the sensor and the ECU reports low EGR flow. It commonly appears alongside a P0325 knock-sensor 'ghost' code. This is a classic emissions-inspection failure item on these cars.
Common Symptoms
- Check engine light
- Failed emissions/inspection
- Occasional rough idle
- P0400 with intermittent P0325
How to Fix
Remove the EGR tube/passage and the EGR temperature sensor, then clear the carbon with a pick and carburetor cleaner; clean the ports and passages rather than replacing the valve. Inspect/replace the EGR temp sensor if damaged. Full EGR valve replacement is only needed if the valve itself is stuck.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- CRC throttle body and air intake cleaner 05078
Universal solvent consumable, not a vehicle-fit part. Follow label/SDS and service procedure; keep away from sensors, coatings and friction/electrical surfaces not approved by the manufacturer.
- Genuine Nissan EGR valve gasket 14719-38U00
Direct listing covers 1995-1999 VQ30DE Maxima; confirm VIN and disassembly path.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
P0400 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0400 mean on a Nissan?
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. On Nissan it is documented across 1 model: Maxima.
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 on a Nissan?
Published repair estimates on Nissan range from $80 to $300 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.
Looking for P0400 on a different make?
View P0400 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.