AutoCodes – Generic – P0684

P0684 Code - Glow Plug Control Module to ECM Communication Circuit Range/Performance

Quick Answer

The Engine Control Module (ECM) monitors the Glow Plug Control Module (GPCM). Common causes include Faulty Glow Plug Control Module (GPCM), GPCM harness is open or shorted, GPCM circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0684 indicates Glow Plug Control Module to ECM Communication Circuit Range/Performance.
Common causes: Common causes include Faulty Glow Plug Control Module (GPCM), GPCM harness is open or shorted, GPCM circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 14,241

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 05, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0684 Description

The Engine Control Module (ECM) monitors the Glow Plug Control Module (GPCM). The ECM sets the OBDII code when can not communicate with the Glow Plug Control Module.

OBDII Code P0684 - Glow Plug Control Module to ECM Communication Circuit Range/Performance - AutoCodes.com — P0684 Code - Glow Plug Control Module to ECM Communication Circuit Range/Performance

What does this mean?

What are the Possible Causes of the DTC P0684?

Faulty Glow Plug Control Module (GPCM)
GPCM harness is open or shorted
GPCM circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0684?

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 P0684 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 P0684 code?

Need more information on how to fix the P0684 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0684 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P0684 Volkswagen — Glow Plug Control Module- Implausible Signal

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 P0684 Code

1. What are the common symptoms of OBDII code P0684 related to Glow Plug Control Module to ECM communication?

- Common symptoms include hard starting, rough idle, reduced engine power, and the illumination of the Check Engine light.

2. What are the possible causes of OBDII code P0684?

- Possible causes include a faulty glow plug control module, damaged wiring or connectors in the communication circuit, or a malfunctioning Engine Control Module (ECM).

3. How can I diagnose the issue causing OBDII code P0684?

- Diagnosis typically involves checking the wiring and connectors for damage, testing the glow plug control module, and using a scan tool to communicate with the ECM for any communication errors.

4. Can I still drive my vehicle with OBDII code P0684?

- It is not recommended to drive your vehicle with this code as it can lead to engine performance issues and potential damage. It's best to address the issue promptly.

5. Is it safe to clear the OBDII code P0684 and see if it returns?

- While clearing the code may temporarily turn off the Check Engine light, it is not a permanent solution. The underlying issue causing the code should be diagnosed and repaired to prevent further problems.

6. How much does it typically cost to repair OBDII code P0684?

- The cost of repair can vary depending on the specific cause of the code and labor rates in your area. It's best to consult a professional mechanic for an accurate estimate.

7. Can a DIY enthusiast fix OBDII code P0684 at home?

- If you have experience with automotive electrical systems and the necessary tools, you may be able to diagnose and repair the issue at home. However, it's recommended to seek professional help if you're unsure.

8. Will OBDII code P0684 affect my vehicle's fuel efficiency?

- Yes, this code can impact fuel efficiency due to engine performance issues. Resolving the underlying problem should help improve fuel economy.

9. How urgent is it to address OBDII code P0684?

- It is important to address this code promptly to prevent further damage to the engine and ensure reliable vehicle operation. Ignoring the issue can lead to more severe problems.

10. Can extreme weather conditions affect the occurrence of OBDII code P0684?

- Yes, extreme cold temperatures can put additional strain on glow plug systems, leading to a higher likelihood of issues related to glow plug control module communication.