◆OBD Codes

P0405

Exhaust Gas Recirculation Sensor "A" Circuit Low

Moderateegr

Overview

The P0405 code indicates the PCM has detected a exhaust gas recirculation sensor "a" circuit low 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

  • Failed emissions test
  • Rough idle
  • Engine knocking or pinging
  • Check Engine Light (MIL) illuminated

Common Causes

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

Diagnosis Steps

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

BMW Diesel modelsToyota TacomaChevrolet DuramaxVolkswagen TDI models

Related Codes

P0403P0402P0401

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
P0406Exhaust Gas Recirculation Sensor "A" Circuit High
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.