P0401 on Honda: How to Diagnose & Fix
Exhaust Gas Recirculation Flow Insufficient
1 Honda model · 1 documented issue · $20-$600 repair
P0401 on Honda by model: symptoms, diagnosis and fix
On the first-generation Honda Insight (2000-2006) with the lean-burn engine, carbon builds up in the exhaust gas recirculation (EGR) system. Both the EGR valve and the EGR plate collect carbon. A retrospective on the car says the lean-burn system "created massive carbon issues with EGR plate and EGR valve requiring frequent maintenance 20-30k miles." The same source says the lean-burn system could run air-fuel ratios as lean as 20:1. When the EGR valve and passages clog, the car can idle roughly, hesitate, lose fuel economy and set a check-engine light (P0401). CVT Insights did not have the lean-burn engine.
Common Symptoms
- Rough idle or stalling
- Hesitation during acceleration
- Poor fuel economy (MPG drops)
- Check engine light with P0401 code
- Engine runs rough in lean burn mode
- Loss of power
How to Fix
What to check first: if the check-engine light is on with code P0401 (EGR flow), inspect both the EGR valve and the EGR plate for carbon. The cited retrospective names both parts, so clean the plate passages as well as the valve. Cleaning: remove the EGR valve, soak it in carburetor cleaner, and clear the passages with a wire brush. Prevention: the cited retrospective treats EGR plate and valve service as regular maintenance on lean-burn cars, roughly every 20,000-30,000 miles.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda 18715-PB2-000 EGR valve gasketOEMHonda 18715-PB2-000
Confirm VIN and current service procedure before disassembly.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipDIY EGR cleaning: Remove valve (2 bolts), soak in carb cleaner overnight, scrub with wire brush. Takes 1 hour, saves $200-300.
- WarningClogged EGR overheats catalytic converter and kills it - clean EGR every 60k miles to avoid $1,500 cat replacement.
Sources for this issue (1)
P0401 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 P0401 mean on a Honda?
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 Honda it is documented across 1 model: Insight.
What are the most common causes of P0401?
The most common causes of P0401 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0401 on a Honda?
Published repair estimates on Honda range from $20 to $600 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.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.