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Summary
  • Diagnostic trouble code (DTC) P0677 stands for “Cylinder #7 Glow Plug Circuit.”
  • The powertrain control module (PCM) will set the P0677 code if it detects an issue with the glow plug circuit in cylinder #7.
  • Common causes of the P0677 code include a faulty glow plug in cylinder #7, an open or shorted glow plug circuit, and faulty wiring connectors.
  • The symptoms of a P0677 code are an illuminated check engine light, starting problems in cold weather, and the preheat light failing to turn on.

When a diesel engine is cold, it can be hard to start because there isn’t enough heat to ignite the air-fuel mixture. It’s the glow plugs’ job to preheat the cylinders to help the engine initiate combustion. If the powertrain control module (PCM) detects an issue with the glow plug in cylinder #7, code P0677 will be logged by on-board diagnostics (OBD).

What Does the P0677 Code Mean?

Diagnostic trouble code P0677 stands for “Cylinder #7 Glow Plug Circuit.”

When a fuel and air mixture is combusted, it produces heat that forces the engine’s pistons to rotate the crankshaft. A diesel engine with a pre-combustion chamber uses a glow plug to initiate the combustion process during cold starts. Some diesel engines with direct injection also rely on glow plugs.

cylinder head of a car
If the PCM detects a fault in the glow plug circuit in cylinder #7, it will log a P0677 code.

The glow plugs are controlled by the PCM, which monitors coolant and air intake temperature. When this electronic device is turned on, it becomes extremely hot and warms the combustion chamber (or pre-chamber) just enough to ignite the incoming fuel. The resistance of the heating element inside the glow plug increases, reducing the current in amperes.

The PCM will also activate the glow plugs to reduce unburned fuel and improve idle quality shortly after starting the engine. If the PCM detects a fault in the glow plug circuit in cylinder #7, the computer will log a P0677 code.

Note: The definition of code P0677 might 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 P0677 Code?

car glow plug
A malfunctioning glow plug in cylinder #7 can cause the P0677 code.

What are the Common Symptoms of the P0677 Code?

  • Illuminated check engine light
  • Starting problems in cold weather
  • The preheat light doesn’t turn on
  • Low power until the engine is sufficiently warmed up

How to Diagnose the P0677 Code

DTC P0677 is a generic powertrain code that applies to vehicles with OBD-II. However, specific diagnostic steps are needed to troubleshoot this code. You’ll need to review your vehicle’s repair manual to figure out the appropriate fix.

Diagnosing your vehicle can be tricky. If you haven’t done it before, we recommend hiring a trained professional to help you out. The following video can be used as a guide if you plan on diagnosing this code yourself.

How to Fix the P0677 Code

There’s no magic bullet that will resolve trouble codes. You have to take your vehicle’s make and model into consideration when researching its recommended diagnostic and repair steps. Luckily, there are a lot of resources online to help you get started. A Chilton repair manual or an ALLDATA subscription provides vehicle-specific information. You can also browse the internet for technical service bulletins related to your vehicle’s issues to save time.

If you don’t have the technical expertise to address this code, you should take your vehicle to the nearest repair shop and have a mechanic run tests to find the right solution.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Contact Center Manager and Technical Reviewer at CarParts.com

William “Bill” Guzenski has produced hundreds of how-to videos for the automotive community. He’s an ASE Certified Master Automobile Technician, and is affiliated with the Specialty Equipment Market Association (SEMA). He loves attending race events and car shows throughout the country, as well as traveling in his 40-foot motorhome, exploring abandoned mines and ghost towns.

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.

File Under : OBD-II Trouble Codes
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