P0677 code definition
The P0677 trouble code marks an issue with the glow plug circuit in cylinder 7
What the P0677 code means
The P0677 code is a standard OBD-II trouble code that detects an issue with the glow plug circuit in cylinder 7. Each cylinder in a diesel engine has a glow plug, which is used to heat the engine and help ignition. The glow plugs are controlled by the powertrain control module (PCM), and when the PCM detects a voltage reading from the cylinder 7 glow plug circuit that deviates from the manufacturer’s specifications by more than 10 percent, the P0677 code will be triggered.
What causes the P0677 code?
Potential causes of the P0677 trouble code are:
- Faulty glow plug relays
- Faulty glow plug timer or module
- Defective glow plug in cylinder 7, or possibly in another cylinder
- Defective electrical components in the glow plug circuit, including wires, connectors, and fuses
What are the symptoms of the P0677 code?
When the P0677 trouble code is detected, the Check Engine Light and glow plug indicator warning light will both likely illuminate on the vehicle’s instrument panel. It is likely that the vehicle will take longer than usual to start, especially when the weather is cold. When the vehicle does start up, it may produce white smoke from the exhaust system.
How does a mechanic diagnose the P0677 code?
The P0677 code should be diagnosed with an OBD-II trouble code scanner. A trained technician will look at the freeze frame data on the scanner to assess the code, and to check for the presence of any other trouble codes. If the mechanic finds that multiple trouble codes are present, then they will be addressed in the order in which the scanner displays them. The codes will then need to be reset, and the vehicle restarted, so the mechanic can check to see if the P0677 code returns. If it does not, then it was likely triggered accidentally, or represents an intermittent error.
If the code remains detected following the reset, then the mechanic will begin by visually inspecting the electrical components in the glow plug circuit. Any wires that are shorted, connectors that are open or corroded, or fuses that are blown will need to be replaced.
Following the electrical inspection, the glow plugs will need to be checked, and possibly replaced. The mechanic can check the glow plugs by connecting one end of a fully charged battery to the glow plug, and the other end to the ground. If the glow plug is incapable of producing heat (or, conversely, heats so intensely that it turns red), then it is defective. The glow plugs can also be inspected with a digital volt/ohmmeter. The mechanic will first inspect the glow plug in cylinder 7, but all glow plugs should be inspected if the issue is not resolved. If the code remains detected following the glow plug inspections and replacements, then the timers and relays will require inspection.
After any component is replaced, the mechanic will need to pause the inspection to once more reset the trouble codes, restart the vehicle, and check to see if the P0677 code remains. This allows the technician to know as soon as the issue is resolved.
Common mistakes when diagnosing the P0677 code
The most frequently made error when diagnosing this code comes from failing to correctly follow the OBD-II trouble code diagnosis protocol. It’s important for mechanics to follow the protocol step by step, as this guarantees an efficient and thorough diagnosis.
Timers and relays are regularly repaired erroneously, when the error is actually a defective glow plug, or faulty fuses, wires, or connectors.
How serious is the P0677 code?
A vehicle with a detected P0677 trouble code will still be drivable, though it will usually have a difficult time starting. If enough glow plugs become defective, the vehicle may be incapable of starting, so the code should be inspected and repaired sooner rather than later.
What repairs can fix the P0677 code?
Common repairs for the P0677 trouble code include:
- Replacement of the glow plug in cylinder 7, or the other cylinders
- Replacement of the electrical components in the system
- Replacement of the glow plug timer or relay
Additional comments for consideration regarding the P0677 code
As glow plugs are only found in diesel engines, the P0677 trouble code only applies to diesel vehicles. It is also common for this code to be joined by additional glow plug circuit trouble codes.
Need help with a P0677 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.