P0404 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts running much worse, stalls, or the warning light flashes.
!The vehicle begins to overheat, knock, or lose power sharply while the code is active.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Check whether the engine idles rough, pings, or feels different when the EGR opens
2
Free - no tools
Inspect the valve, passages, and connector for carbon buildup or damage
3
Basic tool needed
Notice whether the code appeared after long highway use, short-trip driving, or recent intake work
4
Basic tool needed
If scan data is available, compare commanded EGR with actual response before replacing the valve
5
Basic tool needed
If the system uses a position sensor, check its wiring and signal behavior too

If the code returns

-If cleaning the passages changes the behavior, carbon is a stronger suspect than the valve itself.
-If the signal is erratic or stuck, the position sensor or wiring moves higher on the list.
-If the code returns after repair, revisit control, feedback, and vacuum routing before replacing more parts.

Background

What this code means

P0404 is a generic OBD-II code for an EGR range or performance fault.

The ECU can see some EGR activity, but the response is not what it expected at the right time or under the right load.

Diagnosis

Common causes

Most common

Carbon buildup in passages

Deposits can make EGR response slow or inconsistent.

Common

Sticky EGR valve

The valve may move, but not at the right speed or amount.

Common

Position sensor fault

The ECU may not be seeing the valve move as expected.

Possible

Control side issue

The command path may be wrong even if the valve is usable.

Avoid these mistakes

What not to do

xDo not replace the sensor or valve first if there is obvious wiring, connector, or vacuum damage.
xDo not ignore drivability changes just because the code sounds like an emissions fault.

Parts

Parts that may need replacing

PartTypical costNotes

EGR valve$70-$250Relevant when the valve is slow, sticky, or unresponsive.

EGR gasket or passage cleaning$20-$150Often needed if carbon buildup is affecting flow.

EGR position sensor or wiring repair$30-$150Useful if the feedback side is not believable.

Related OBD codes

P0400

P0400 usually means the EGR system is not flowing exhaust gas the way it should.

P0403

P0403 usually means the EGR control circuit has a malfunction.

P0405

P0405 usually means the EGR position sensor is reading too low.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0404 was expanded around common EGR range/performance faults, especially carbon buildup, sticky valves, and sensor feedback problems.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0404 - P0404 Usually Means the Egr System Is Out of Range or Performing Poorly