Error Code P0684: What It Means & What To Do?

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A sudden increase in the fuel consumption and the engine performance along with occasional engine stalling and not starting with improper throttle response may be an indication of problem with the glow plug and starting system hampering the engine’s performance, thus indicating OBD Code P0684.

OBD-II Code Hard or no start in cold weather is defined as a Glow Plug Control Module to PCM Communication Circuit.

OBD II fault code P0684 is set when the PCM (Powertrain Control Module) detects a failure of the glow plug control module itself, a failure in one or more of the circuits that supply the glow plug control module with power, or a failure in one or more monitoring/communication/signal circuits that connect the glow plug control module with other control modules in the CAN (Controller Area Network) bus system. Note that on some applications, “circuit malfunction” could also mean that a circuit failure exists between the glow plug control module and one or more individual glow plugs.

The purpose of glow plugs on diesel engines is to provide a source of intense heat to assist in the combustion process of the air/fuel mixture when the engine is cold, or below a minimum threshold temperature. This pencil-shaped component heats up and glows up for about 10 seconds. This results in an increase in the temperature of the surrounding wall, allowing heat compression to rise for the ignition.

What causes this problem with the Glow Plug Control Module to PCM Communication Circuit Range/Performance?

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
• Blown fuse(s) and/or blown fusible links
• Failed Glow Plug Control Module
• Defective glow plug-, or other control module and/or circuit that monitors/controls/regulates some aspect of glow plug control
• Defective engine coolant sensor(s)
• Defective ignition switch
• One or more defective glow plugs
• Failed or failing PCM

1. Glow Plug - Faulty glow plug will not heat up properly, being insufficient to raise the temperature and assisting in the ignition. Buy and replace old faulty glow plugs now!
2. Glow Plug Relay - Glow plug relay can also be damaged or faulty and might require replacement. Buy new glow plug relay and replace the faulty one now!
3. Engine Control Module - OBD Error Code P0684 can also be due to faulty ECMs. It’s better to get the faulty electricals replaced as soon as possible.
4. Powertrain Control Module - P0684 error code also relates to problems with the powertrain that is not able to generate response in time causing distorted engine timing. Find all the Powertrain related parts with us.
5. Diagnostic Tool - In order to detect the error, one needs high grade diagnostic tools. Visit us today to grab amazing deals.
6. Battery - Check for the car battery is faulty or not and repair or replace as required. Buy new car batteries form us. Buy now!

It is vital to know the symptoms of an issue as only then you would be able to solve the problem. So that’s why we have listed out some major symptoms of OBD Code P0684 here:

Common Symptoms

• Engine Light ON (or Service Engine Soon Warning Light)
• Lack/Loss of Power
• The engine may be harder to start
• Engine hesitation
• White smoke from the exhaust
• Affected fuel consumption

Once you know the symptoms of your vehicle’s problem, it becomes easy to detect it and get started with solving it. So, next on our list is few common steps to correct this issue with your vehicle.

• Change or car battery
• Damaged connectors and wires replacement
• Glow Plug Computer Module replacement
• Glow plug relay replacement
• PCM replacement

However, if you face any issue then we have stocked a wide range of best priced Glow Plug Relay, Glow Plug Circuit, Powertrain Control Module, Engine Control Module, Glow Plug Control Module Harness and more to help you out in fixing your car.

A qualified technician who has the knowledge of industrial grade diagnostic tools should be recommended for the diagnosis Error P0684. Proper checks of the wirings and connectors as well as circuits, ECM/PCM, ignition system, etc., should be done. Following are some points to be taken care of during the diagnosis.

• A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in trying to perform a successful diagnosis.
• Begin with a visual inspection of all wiring and connectors. Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary.
• An experienced technician with a specialized scanner may determine the general area of the malfunction much more rapidly and easily than someone using a code reader and a digital volt ohmmeter.
• Disconnecting and testing every single pin of the CAN bus could prove to be extremely time and cost prohibitive. Use a specialized diagnostic CAN scanner to see pin values and control module operation without risking a meltdown. It will help to accurately diagnose computer and circuitry problems by monitoring vehicle operation while the vehicle is being operated.
• Look for loose or corroded electrical connectors that may increase circuit resistance and cause these types of codes to be stored. Obtain a CAN bus system wiring diagram and/or pin out value chart, then use the digital volt ohmmeter to test continuity between individual controller connectors and compare your findings with the manufacturer’s referenced values and repair open or shorted circuits as required.
• Check for defective glow plugs, glow plug relay, harness, connectors and other hardware leading to the control module not functioning properly and replace as required.

Common Mistakes When Diagnosing the P0684 Code

Some of the common mistakes done while changing diagnosing the OBD code P0684 are:

• Improper assessment of the Glow Plug Control Module
• Simply replacing the Powertrain Control Module (PCM) without considering other possibilities of problem
• Not noticing the damaged or loosened wiring and circuit problems

P0683 - Glow Plug Control Module to PCM Communication Circuit