How is fault code P0404 fixed?

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Read live data on commanded vs actual EGR position, the gap tells you whether the valve is responding to commands 2. Remove the EGR valve and visually inspect, carbon buildup is usually obvious and dramatic 3. Try cleaning if accessible, EGR cleaner spray (£8) and patience often restores function for another 20,000-50,000 miles 4. Test the actuator electrically against spec, resistance and operation against manufacturer values 5. If cleaning doesn't free the valve, replacement is the next step 6. On diesels, address the underlying cause (short-trip driving, carbon-heavy intake) at the same time, otherwise the new valve clogs up just as fast

Exhaust Gas Recirculation Circuit Range/Performance

Jump to the fix

Severity

Low

Can I keep driving?

Usually drivable; have it fixed at the first opportunity.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Read live data on commanded vs actual EGR position, the gap tells you whether the valve is responding to commands 2. Remove the EGR valve and visually inspect, carbon buildup is usually obvious and dramatic 3.

PPowertrain
0Generic code
4Emissions
04Sequence number

What does it mean?

P0404 is a generic OBD II fault code that indicates that there is an issue with the Exhaust Gas Recirculation (EGR) circuit. The Engine Control Module (ECM) has detected that the EGR circuit is either out of range or not functioning properly. The purpose of the EGR system is to burn fuel more efficiently. The exhaust gases are routed back to the intake for combustion again. This process lowers emissions and increases fuel economy. There are several symptoms that identify an Exhaust Gas Recirculation problem.

Symptoms

Likely causes

How to fix it

Codes From the Same System

All Fault Codes

Related Similar Codes

This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.