P0401 — EGR insufficient flow detected
Exhaust gas recirculation isn’t flowing as commanded — clogged passages or a bad EGR valve are common.
What it means in plain English
P0401 means the computer commanded EGR flow and didn’t see the expected result. Carbon-clogged EGR passages and failed EGR valves are frequent, especially on higher-mileage engines. Some designs use differential pressure sensors that also fail.
Common causes
- Carbon buildup in EGR passages
- Faulty EGR valve
- EGR pressure / position sensor issues
- Vacuum supply problems on vacuum-operated systems
What you can safely check
- Note pinging/knock under light load if present.
- Don’t dismantle EGR plumbing without a service guide — hot exhaust parts and broken bolts are common.
Pull the code yourself (disclosed)
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A reusable Bluetooth OBD-II scanner lets you read the code and freeze-frame data before authorizing “mystery” diagnostics. One option: BlueDriver Bluetooth Pro OBD-II scan tool (BlueDriver/Levanta affiliate). Any capable OBD-II reader is fine — this is not required to use Fair Auto Shops.
When to go to a shop
Ask whether passages will be cleaned when a valve is replaced. A new valve on clogged ports often returns the code.
Typical related repair costs (U.S. national averages)
These are related repairs shops may find after diagnosis — not a guaranteed bill for every P0401. Ranges exclude taxes, fees, diagnostics, and your location.
- $489–$632 national average for EGR valve replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $181–$265; parts $308–$367.
Related cost guides: Egr Valve
Questions to ask before you authorize work
Use questions before you authorize a repair and how to read a repair estimate. Watch for patterns in spotting upselling.
Find an honest independent shop
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FAQ
What should I do first with a P0401 code?
Photograph all codes, note symptoms and whether the light is flashing, avoid clearing data until a shop sees it, then use an independent shop with a clear diagnostic plan.
More check-engine codes
P0420 · P0430 · P0300 · P0301 · P0171 · P0174 · P0455 · P0456 · P0442 · P0446 · P0128 · P0133 · P0113 · P0506 · P0507 · P0700 · P0741 · P0011 · P0325 · P0340 · P0335 · P0101 · P0299 · P0135 · P0440 · P0441 · P0010 · P0500 · P0121
Hub: How to read a check-engine code · Repair cost guides · Affiliate disclosure