P0404 means the EGR valve is responding to ECU commands, but not within the expected position range. The ECU asks for a specific opening (say 30%) and the position sensor reports something different. Carbon buildup restricting valve travel is by far the most common cause.
P0404 means the EGR valve is responding to ECU commands, but not within the expected position range. The ECU asks for a specific opening (say 30%) and the position sensor reports something different. Carbon buildup restricting valve travel is by far the most common cause.
P0404 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0404 and illuminates the check engine light.
If your vehicle has triggered P0404, you may notice one or more of these symptoms:
Here are the most common causes of P0404, ranked by how likely they are to be the culprit:
Generally yes, for short-term driving. Driveable. P0404 means the EGR valve is moving, but its actual position does not match what the ECU commanded. Expect rough idle, possible hesitation, and a failed emissions test. Some diesels limit power to protect the DPF and SCR systems.
Follow these steps to pinpoint the root cause of P0404:
Repair costs for P0404 vary depending on the root cause and your vehicle. Here are typical estimates:
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0404 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
These codes are often seen alongside P0404 or indicate related issues:
P0403 is a pure electrical circuit fault (open, short, no response). P0404 means the circuit works, but the valve position does not match the commanded position. P0404 is almost always mechanical (carbon buildup, sticking pintle), while P0403 is usually electrical (solenoid, wiring, connector).
Yes, short-term. Some modern diesels go into limp mode if the EGR cannot reach commanded positions, because the after-treatment calibration relies on EGR for NOx control. Plan the repair within a few weeks to avoid secondary DPF or SCR codes.
On petrol engines, often yes if you also clean the intake manifold passages. On diesels with heavy soot output (BMW N47/B47, VAG EA189), cleaning may only last 20,000–40,000 km before the code returns. If the EGR cooler is degraded, replacement of the cooler-valve assembly is more durable.
Yes on most modern vehicles. BMW, Mercedes, and VAG all use stored adaptation values that must be reset and re-learned after a new EGR valve is fitted. INPA, VCDS, or a similar bi-directional scan tool is required. Skipping this step often causes the new valve to throw P0404 again within a few drive cycles.
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