P0677 Code: Cylinder #7 Glow Plug Circuit

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.

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?

• Defective glow plug in cylinder #7
• Open or shorted glow plug circuit
• Bad wiring connector
• Faulty glow plug control module

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.