P0406 medium Severity

P0406: Exhaust Gas Recirculation Sensor A Circuit High

May not immediately prevent normal operation, but can increase emissions and potentially reduce engine performance or fuel economy.

Overview

P0406 indicates that the EGR position sensor circuit 'A' is reporting a voltage higher than the expected range, suggesting a high signal from the EGR position sensor or associated wiring/circuit faults in the exhaust gas recirculation system.

Common Symptoms

  • Check engine light (MIL) illuminated
  • Increased NOx emissions
  • Reduced fuel economy
  • Possible rough idle or intermittent stall
  • Engine performance concerns such as surging

Most Common Causes

Faulty EGR position sensor high

Sensor output voltage above specified range triggers code.

Damaged or corroded wiring/connectors in EGR circuit high

Wiring issues can cause incorrect voltage feedback.

EGR valve mechanical issues or carbon buildup medium

Sticking valve may alter sensor feedback or EGR flow.

EGR sensor signal circuit shorted to battery or reference voltage medium

Circuit short can cause high voltage reading.

PCM internal fault or software issue low

Less common cause but possible if other causes are ruled out.

Diagnostic Steps

  1. Confirm code and check for additional DTCs using an OBD-II scanner
    Expected: Only P0406 present or related codes
    Interpretation: Ensures focused diagnosis on EGR sensor circuit.
  2. Visually inspect EGR position sensor wiring and connectors for damage or disconnection
    Expected: No frayed wires, corrosion, or loose pins
    Interpretation: Wiring issues often cause high voltage feedback.
  3. Measure EGR position sensor voltage signal with a multimeter
    Expected: Signal within manufacturer specified range (e.g., ~0.4–4.5 V)
    Interpretation: High voltage confirms sensor or circuit fault.
  4. Inspect EGR valve for carbon buildup or mechanical sticking
    Expected: Valve moves freely and passages are clean
    Interpretation: Mechanical issues can affect sensor readings.
  5. If wiring and EGR are good, consider PCM software update or internal fault diagnosis
    Expected: No improvement after other fixes
    Interpretation: PCM issues are lower likelihood but possible.

Repair Solutions

Replace faulty EGR position sensor medium
Estimated Cost: $150 - $400

Sensor cost and labor varies by vehicle make/model.

Repair or replace damaged wiring/connectors medium
Estimated Cost: $50 - $200

Depends on extent of wiring issue.

Clean EGR valve and passages medium
Estimated Cost: $70 - $250

Carbon buildup removal may restore proper operation.

Replace EGR valve if mechanically faulty medium
Estimated Cost: $200 - $500

Often vehicle-specific pricing.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Replacing EGR valve without inspecting wiring or sensor circuit

Frequently Asked Questions

What does the P0406 code mean?

Exhaust Gas Recirculation Sensor A Circuit High is the standard definition for P0406. This diagnostic code is triggered when the ECU detects a problem in the Emissions.

Should I stop driving if I have P0406?

This is a medium priority issue. May not immediately prevent normal operation, but can increase emissions and potentially reduce engine performance or fuel economy.

What happens when the P0406 code is active?

The most typical signs are: Check engine light (MIL) illuminated, Increased NOx emissions, Reduced fuel economy.

Why is my car throwing a P0406 code?

This code is frequently triggered by: Faulty EGR position sensor, Damaged or corroded wiring/connectors in EGR circuit, EGR valve mechanical issues or carbon buildup.

Is P0406 expensive to fix?

Expect to pay around $200 if the issue is a Repair or replace damaged wiring/connectors, but up to $500 if the Replace EGR valve if mechanically faulty needs replacement.

Is P0406 a generic or manufacturer-specific code?

The P0406 code is a generic powertrain code, meaning it applies to almost all makes and models, such as Honda, Toyota, VW, Ford, and Chevy.

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