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Are you having trouble starting your diesel engine? You may want to connect a scan tool to see if there are any trouble codes logged. If the P0678 code has been triggered, read this article for everything you need to know about its definition, common causes, and common symptoms.

What Does the P0678 Code Mean?

Diagnostic trouble code (DTC) P0678 code stands for Cylinder #8 Glow Plug Circuit/Open. The powertrain control module (PCM) triggers the P0678 code when it detects the glow plug in cylinder 8 isn’t operating properly. Diesel engines need the glow plug to heat the combustion chamber before the engine is started. Unlike gasoline, which can readily ignite in most conditions just by introducing a spark, diesel fuel can only ignite when it reaches its flash point temperature. A faulty glow plug can prevent diesel from igniting in cold weather conditions.

installing a glow plug
The PCM triggers the P0678 code when it detects the glow plug in cylinder 8 isn’t operating properly.

Note: The definition of the P0678 code can be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0678 Code?

Code P0678 might show the following symptoms:

  • Faulty glow plug in cylinder #8
  • Circuit issues, such as a damaged wire or poor connection
  • Faulty control module

What are the Common Symptoms of the P0678 Code?

The check engine light will likely illuminate as soon as the PCM detects a faulty glow plug. There might not be any immediate symptoms since the engine can still start if there’s only one faulty glow plug. However, you’re more likely to experience the following symptoms if the weather is cold:

driver starting a car
Difficulty starting the engine is a common symptom of code P0678.

How to Diagnose the P0678 Code

The P0678 code’s definition does point to a faulty glow plug in cylinder number eight. However, there’s a chance that this isn’t always the issue. When it comes to fixing DTCs, you must first accurately diagnose the problem before you do any fixes. The concerned components will likely need to be inspected or tested to find the root cause. This task might require specialist equipment or knowledge, so it’s best to leave it to a professional mechanic.

Want to learn how you can diagnose the problem yourself? Check out the video below:

How to Fix the P0678 Code

There isn’t a single procedure that can fix the problems that trigger your vehicle’s stored OBD-II code. Depending on the defective component and vehicle design, the repair procedure can vary. The best solution is to do a thorough inspection before executing a repair. You can consult various internet vehicle repair resources and how-to guides for possible solutions when you’ve correctly identified the problem. You should also remember that your vehicle’s owner’s manual can contain valuable troubleshooting tips.

Chilton repair manuals can also be useful. ALLDATA subscriptions , on the other hand, may be better because they include specific factory repair information for drivers who wish to perform their own repairs.

If you don’t have much experience diagnosing or repairing error codes, it’s best to consult a professional mechanic.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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