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

Overview

P0402 is an OBD‑II trouble code indicating the vehicle’s engine control module has detected excessive exhaust gas recirculation flow, typically related to the EGR system malfunction.

Common Symptoms

Check Engine Light illuminated
Rough or unstable idle
Engine hesitation or stalling
Reduced acceleration or power
Decreased fuel economy
Failed emissions test

Most Common Causes

Stuck open or faulty EGR valve high

Valve may not close properly, allowing excessive EGR flow.

Faulty Differential Pressure Feedback EGR (DPFE) sensor or equivalent pressure sensor high

Sensor may give incorrect readings leading to false detection of excessive flow.

Vacuum leak or failed EGR control solenoid medium

Vacuum issues can cause uncontrolled EGR valve operation.

Carbon buildup or clogged EGR passages medium

Blockages can disrupt proper EGR regulation.

Faulty EGR wiring or connectors low

Electrical issues can lead to improper EGR operation.

Diagnostic Steps

Connect an OBD‑II scan tool and confirm the P0402 code

Expected: P0402 stored with freeze frame data

Interpretation: Confirms the code is present and records engine conditions when triggered.
Inspect EGR valve and passages for carbon buildup or blockages

Expected: Presence or absence of carbon buildup

Interpretation: Carbon buildup may cause improper EGR flow leading to code.
Test EGR valve operation (vacuum or electronically actuated)

Expected: Valve actuates correctly within specifications

Interpretation: Proper functionality excludes valve mechanical failure.
Check DPFE or EGR pressure sensor readings using live data

Expected: Sensor values within manufacturer range

Interpretation: Out‑of‑range values point to sensor fault.
Inspect vacuum lines and EGR solenoid wiring

Expected: No leaks or damaged wires

Interpretation: Leaks or electrical faults can cause uncontrolled EGR flow readings.

Repair Solutions

Replace or service EGR valve medium

Estimated Cost: $200 - $600

Valve replacement or cleaning can resolve mechanical sticking issues.

Replace DPFE or EGR pressure sensor medium

Estimated Cost: $90 - $300

Sensor replacement is often necessary when readings are incorrect.

Repair vacuum leaks and replace faulty solenoid medium

Estimated Cost: $100 - $400

Ensures proper EGR control and operation.

Clean EGR passages and remove carbon buildup hard

Estimated Cost: $80 - $200

Labor intensive; may prevent recurrence.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

Ignition system faults
Fuel delivery issues
Oxygen sensor faults

Frequently Asked Questions

Technical definition of P0402 OBD-II Code

Exhaust Gas Recirculation (EGR) Flow Excessive Detected is the standard definition for P0402. This diagnostic code is triggered when the ECU detects a problem in the Emissions.

Is it safe to drive with a P0402 code?

With a severity level of medium, may cause rough idle, engine hesitation or stalling, reduced power, and emission failures; check engine light illumination.

Symptoms associated with DTC P0402

Drivers often report: Check Engine Light illuminated, Rough or unstable idle, Engine hesitation or stalling when this code is present.

What causes the P0402 code?

The most common causes are: Stuck open or faulty EGR valve, Faulty Differential Pressure Feedback EGR (DPFE) sensor or equivalent pressure sensor, Vacuum leak or failed EGR control solenoid.

What is the price difference for fixing P0402?

It depends on what needs to be fixed. Clean EGR passages and remove carbon buildup repairs are cheaper (~$200), while Replace or service EGR valve repairs are on the higher end (~$600).

Is the P0402 code specific to Mercedes?

P0402 is not specific to any one brand. It can appear on Ford, Dodge, Toyota, Honda, Jeep, and other vehicles.

P0402: Exhaust Gas Recirculation (EGR) Flow Excessive Detected