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P0684 is a diagnostic trouble code (DTC) for "Glow Plug Control Module to PCM Communication Circuit Range/Performance". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0684 OBD-II Trouble Code indicates that the glow plug control module to PCM communication circuit has a problem in the range/performance area of communications.
The P0684 code means that there is a fault within the powertrain control module, the PCM, which will not allow it to communicate and send commands to the glow plug control module. This code does not determine the part of the system that has the problem. It merely indicates that there is a failure somewhere in that system. In some cases, the P0670 trouble code can occur along with this cost. This indicates that there is an issue with the wiring harness from the GPCM to the solenoid.
A number of different things can cause the P0684 code to appear. The common causes associated with this trouble code include the following:
If your vehicle has a P0684 Code showing, then you may notice certain symptoms affecting your vehicle. You will notice that your Check Engine Light is on and the code is set. If there are only one or two failed glow plugs, then you might not notice many changes in the way the vehicle performs. However, if the engine is cold, it might be difficult to start. It could also have a miss until it has warmed up enough. If more than two glow plugs are affected by the issue, it will be extremely difficult to start the engine.
The mechanic will utilize a tool called an OBD-II scanner. This tool connects to the vehicle and the Onboard Diagnostics II system they have on board, and provides help in diagnosing the vehicle, as well as data needed to determine the fault with the vehicle and the steps needed for repair. The technician will check the data, reset the code, and then test the vehicle to see if the code returns. If it doesn’t return, it is likely a false alarm. If it does return, it indicates to the mechanic that he or she needs to perform repairs.
The seriousness of the code will truly depend on the number of glow plugs that have failed. If it is only one or two, the vehicle should still start. More than that, and you will have real trouble. Regardless, when this trouble code appears, you should have a mechanic look at your vehicle.
When a trained mechanic is trying to repair your vehicle and fix the P0684 code, they will first want to determine the true nature of the problem.
As a vehicle ages, it will often have sensor issues, some of which are false alarms and some of which are of legitimate concern. The mechanic’s testing can determine whether you have a real problem or not, so it’s not advisable to skip a visit to the mechanic even if you believe the code is not a real concern.
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.