What happens if I ignore an EGR code?

Ignoring an EGR code can lead to increased NOx emissions, engine knocking, poor fuel economy, and potential engine damage from detonation. It will also cause an emissions test failure.

How much does EGR repair cost?

EGR repairs range from $150 for cleaning to $400-$600 for valve replacement. EGR cooler replacement on diesel engines can cost $800-$1,500.

P0409

Exhaust Gas Recirculation Sensor "A" Circuit

Moderateegr

Overview

The P0409 code indicates the PCM has detected a exhaust gas recirculation sensor "a" circuit fault in the exhaust gas recirculation (EGR) system. The EGR system reduces nitrogen oxide (NOx) emissions by recirculating a controlled amount of exhaust gas back into the intake manifold. An EGR malfunction can cause rough running, engine knocking, and increased emissions.

Symptoms

Check Engine Light (MIL) illuminated
Increased NOx emissions
Rough idle
Failed emissions test

Common Causes

Carbon buildup in EGR valve or passages
Failed EGR cooler
Failed EGR valve (stuck open or closed)
Faulty PCM commanding incorrect EGR operation

Diagnosis Steps

1Connect an OBD-II scanner and read all stored trouble codes and freeze frame data
2Inspect the EGR valve for carbon buildup; clean or replace as needed
3Test the EGR valve operation by applying vacuum or using the scan tool
4Check EGR passages for carbon blockage
5Test the EGR position sensor and wiring with a multimeter

Estimated Repair Cost

$150 — $600

Cost varies by vehicle, location, and repair shop. Includes parts and labor.

Commonly Affected Vehicles

Ford 6.0L/6.7L DieselRam 1500Ford F-150Nissan Frontier

Related Codes

P0403 P0401 P0405

More Egr Codes

P0400Exhaust Gas Recirculation Flow Malfunction

Moderate

P0401Exhaust Gas Recirculation Flow Insufficient Detected

Moderate

P0402Exhaust Gas Recirculation Flow Excessive Detected

Moderate

P0403Exhaust Gas Recirculation Circuit Malfunction

Moderate

P0404Exhaust Gas Recirculation Circuit Range/Performance

Moderate

P0405Exhaust Gas Recirculation Sensor "A" Circuit Low

Moderate

Frequently Asked Questions

Yes, EGR valves clogged with carbon can often be cleaned using throttle body or EGR cleaner. This is a cost-effective first step before considering replacement.