AutoCodes – GMC – P0402 2018 GMC Sierra

P0402 2018 GMC Sierra Code - Exhaust Gas Recirculation Flow Excessive

Quick Answer

The Exhaust Gas Recirculation (EGR) valve is controlled by the Engine Control Module (ECM). Common causes include Faulty Exhaust Gas Recirculation (EGR) Valve, EGR solenoid valve harness is open or shorted, EGR solenoid valve circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means: P0402 2018 GMC Sierra indicates Exhaust Gas Recirculation Flow Excessive.
Common causes: Common causes include Faulty Exhaust Gas Recirculation (EGR) Valve, EGR solenoid valve harness is open or shorted, EGR solenoid valve circuit poor electrical connection.
Severity: Moderate - service should be scheduled soon.
Can I drive?: The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

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Code Popularity 235

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 19, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0402 2018 GMC Sierra Description

The Exhaust Gas Recirculation (EGR) valve is controlled by the Engine Control Module (ECM). The ECM controls the EGR valve by supplying a 12-volt pulse width modulated signal to the EGR Valve low control circuit and 12 volts to the high control circuit. The ECM monitors the EGR flow performance when the EGR is active by comparing the desired Mass Air Flow (MAF) to the actual MAF. If the difference between the desired MAF and the actual MAF is less than or greater than a calibrated threshold level the amount of detected EGR flow is out of range. The Diagnostic Trouble Code (DTC) will be set when the ECM detects that the difference between the desired mass air flow and the actual mass air flow is less than a calibrated value for greater than 12.5 s.

OBDII Code P0402 2018 GMC Sierra - Exhaust Gas Recirculation Flow Excessive - AutoCodes.com — P0402 2018 GMC Sierra Code - Exhaust Gas Recirculation Flow Excessive

What does this mean?

What are the Possible Causes of the DTC P0402 2018 GMC Sierra?

Faulty Exhaust Gas Recirculation (EGR) Valve
EGR solenoid valve harness is open or shorted
EGR solenoid valve circuit poor electrical connection

How to Fix the DTC P0402 2018 GMC Sierra?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0402 2018 GMC Sierra code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0402 2018 GMC Sierra code?

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0402 2018 GMC Sierra Code

1. What does the OBDII code P0402 mean for a 2018 GMC Sierra?

P0402 indicates that the Exhaust Gas Recirculation (EGR) system is detecting an excessive flow of exhaust gases being recirculated into the intake manifold, which is outside the expected range.

2. What are the symptoms of code P0402 on a 2018 GMC Sierra?

Common symptoms include rough idling, decreased fuel efficiency, poor engine performance, hesitation during acceleration, and the Check Engine Light illuminating.

3. What causes the P0402 code to trigger on a 2018 GMC Sierra?

Possible causes include a stuck-open EGR valve, carbon buildup in the EGR system, a malfunctioning EGR sensor, a faulty EGR solenoid, or a damaged EGR valve gasket.

4. Can a vacuum leak cause the P0402 code on my GMC Sierra?

Yes, a vacuum leak in the EGR system can lead to excessive exhaust gas flow, potentially triggering the P0402 code.

5. How do I fix the P0402 code on a 2018 GMC Sierra?

Common fixes include cleaning or replacing the EGR valve, checking and repairing vacuum lines, replacing the EGR sensor or solenoid, and clearing carbon buildup in the EGR passages.

6. Is it safe to drive with a P0402 code on my GMC Sierra?

Driving with the P0402 code may not cause immediate damage, but it can lead to reduced engine performance, higher emissions, and potential long-term damage if left unresolved.

7. How much does it cost to repair a P0402 code on a 2018 GMC Sierra?

Repair costs depend on the specific issue but typically range from $150 to $400, including parts and labor for cleaning or replacing the EGR valve or related components.

8. Can a dirty air filter cause the P0402 code on a GMC Sierra?

While unlikely, a severely clogged air filter could impact engine performance and exacerbate EGR system issues, contributing to the code.

9. How do I diagnose the P0402 code on a 2018 GMC Sierra?

Diagnosis involves scanning for additional codes, inspecting the EGR valve and related components for damage or carbon buildup, checking vacuum lines, and verifying the EGR sensor's functionality.

10. Will clearing the P0402 code fix the problem on my GMC Sierra?

Clearing the code will turn off the Check Engine Light temporarily, but it will likely reappear unless the underlying issue with the EGR system is resolved.