Emission codes
P0401: exhaust gas recirculation flow insufficient
The EGR system feeds a little exhaust back into the intake to cool combustion and cut nitrogen oxides. P0401 means the computer commanded that flow and did not see the effect it expected.
P0401: can I drive, and what will the labor cost?
Estimated labor, clean carbon from egr valve and passages
$110 to $330
| Labor time (estimate) | 1 to 3 h |
| Rate used | $110/h |
| Technician wage, United States (average) | $27.13/h |
| Moderate: fix within weeks Drivable; the engine may ping under load because cylinders run hotter, and NOx emissions rise. | |
Labor only: parts and the diagnostic fee are not included. Hours are our estimate for a typical car; book times vary by model. Wage: BLS, May 2025.
P0401 is the generic OBD-II code for "exhaust gas recirculation A flow insufficient detected". Under light and moderate load, the EGR valve opens to send a measured amount of exhaust into the intake. The inert gas lowers the peak combustion temperature, which reduces the formation of nitrogen oxides, one of the pollutants the emission standards limit. The computer tests the system by opening the valve and watching for a change: in manifold pressure, in a dedicated pressure feedback sensor on some Ford engines, in temperature, or in fuel trim. When the change is too small, it stores P0401. The most frequent causes are carbon that clogs the passages between the exhaust and the intake, and a valve stuck closed by deposits. A faulty feedback sensor or its hoses come next, then vacuum supply or control solenoid faults on older systems. It is drivable, but cylinders run hotter, which can cause pinging under load and higher NOx at an emissions test.
Is this repair still under the emission warranty?
Catalytic converter
Likely covered: ask a dealer
| Federal emission warranty, 8 years or 80,000 miles | within |
Age counts from delivery to the first buyer; whichever limit comes first ends the warranty. Your warranty booklet lists the covered parts and prevails.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
P0401 at a glance
| Code | P0401 |
| Standard description | Exhaust Gas Recirculation "A" Flow Insufficient Detected |
| System | Exhaust emission controls |
| Severity | Moderate: fix within weeks |
| Common symptoms | pinging under load, emissions test failure |
Why carbon is the usual culprit
Exhaust carries soot and oil vapor. Over many miles of short trips and idling, these bake into hard deposits inside the EGR valve and the narrow ports that lead to each cylinder or to the intake plenum. The valve may still move, but the gas cannot get through. Cleaning the passages, sometimes with the intake removed, often fixes P0401 without any part, which is why the labor table puts cleaning first and gives it a wide range.
Electronic and vacuum valves
Most recent engines use an electric EGR valve with a position sensor. A technician can command it open with a scan tool and watch the idle stumble, a quick sign that gas flows. On older vacuum-operated valves, a hand vacuum pump does the same. If the valve moves but nothing happens, the passages are blocked; if it does not move, the valve or its control is at fault.
Ping and the converter
Without EGR, combustion is hotter and more prone to knock under load. If you hear pinging, use the recommended octane and go easy until it is fixed. NOx is not controlled by EGR alone; the catalytic converter also reduces it, which is why the related pages include P0420. A misfire such as P0300 is unrelated but can be set by the same carbon problems on some engines.
Likely causes of P0401, in order
| Cause | How often |
|---|---|
| Carbon-clogged EGR passages or ports | most frequent |
| EGR valve stuck closed | most frequent |
| EGR pressure feedback sensor (DPFE) or hoses | frequent |
| Vacuum supply or EGR solenoid fault | less frequent |
P0401 repairs and labor time
| Repair | Labor (estimate) | At $110/h |
|---|---|---|
| Clean carbon from EGR valve and passages | 1 to 3 h | $110 to $330 |
| Replace the EGR valve | 0.5 to 2 h | $55 to $220 |
| Replace EGR pressure feedback sensor | 0.3 to 0.6 h | $33 to $66 |