AutoFixDB - Free OBD-II diagnostic trouble code lookup. Find causes, symptoms, diagnostic steps and repair solutions.

Overview

P0405 indicates a low voltage signal detected in the EGR Sensor A circuit, often caused by EGR valve position sensor issues, wiring faults, or carbon buildup affecting emissions control

Common Symptoms

Check Engine Light illuminated
reduced engine performance or sluggish acceleration
rough idle
slightly decreased fuel economy
failed emissions test

Most Common Causes

Faulty EGR valve position sensor high

Sensor does not produce expected voltage feedback to PCM

Damaged or corroded wiring/connectors in EGR sensor circuit high

Wiring short to ground or open circuit causes low signal voltage

Faulty EGR valve (sticking or not opening properly) medium

Valve issue can prevent proper EGR operation leading to false low feedback

Carbon buildup in EGR system medium

Carbon restricting valve movement or sensor function

ECM input circuit fault low

Rare cause but possible when internal ECM input fails

Diagnostic Steps

Connect an OBD-II scan tool and retrieve stored codes

Expected: P0405 stored with possible related codes

Interpretation: Confirms EGR sensor circuit fault
Visually inspect EGR valve wiring and connectors

Expected: No broken wires, corrosion, or loose pins

Interpretation: Wiring problems present if damage or corrosion is found
Using a multimeter, check for presence of 5V reference at EGR sensor

Expected: Approximately 5 volts at reference wire

Interpretation: Missing reference voltage indicates wiring or PCM issue
Measure EGR position sensor signal voltage with ignition on

Expected: Voltage within expected range (typically above ~0.5V)

Interpretation: Low signal voltage confirms sensor or circuit issue
Inspect and clean EGR valve and passages

Expected: Valve moves freely; no heavy carbon build up

Interpretation: Sticking or blockage may cause inaccurate sensor feedback

Repair Solutions

Replace EGR valve position sensor medium

Estimated Cost: $150 - $400

Often resolves low signal voltage issues

Repair or replace damaged wiring/connectors medium

Estimated Cost: $50 - $250

Fix short to ground or open circuits

Clean EGR valve and passages easy

Estimated Cost: $50 - $150

Effective when carbon buildup restricts valve movement

Replace EGR valve assembly medium

Estimated Cost: $200 - $600

Necessary if valve itself fails

Common Misdiagnoses

Avoid these common diagnostic mistakes:

Interpreting low EGR voltage as purely mechanical valve fault without checking wiring or sensor signal

Frequently Asked Questions

What does the P0405 code mean?

Exhaust Gas Recirculation (EGR) Sensor A Circuit Low is the standard definition for P0405. This diagnostic code is triggered when the ECU detects a problem in the Emissions.

Reflecting on severity: How bad is P0405?

This is a medium priority issue. Check Engine Light illumination; possible reduced performance, rough idle, slightly decreased fuel economy; may fail emissions testing

Symptoms associated with DTC P0405

Drivers often report: Check Engine Light illuminated, reduced engine performance or sluggish acceleration, rough idle when this code is present.

What causes the P0405 code?

Potential culprits include: Faulty EGR valve position sensor, Damaged or corroded wiring/connectors in EGR sensor circuit, Faulty EGR valve (sticking or not opening properly). A proper diagnosis is recommended.

Repair cost breakdown for P0405

Repair costs depend on the specific failure. A simple Clean EGR valve and passages replacement is relatively affordable ($50-$150), whereas a Replace EGR valve assembly repair is more expensive, potentially reaching $600.

What cars are affected by the P0405 code?

The P0405 code is a generic powertrain code, meaning it applies to almost all makes and models, such as Honda, Toyota, VW, Ford, and Chevy.

P0405: Exhaust Gas Recirculation (EGR) Sensor A Circuit Low