What is the P0684 fault number? What is the Glow Plug Control Module-PCM Communication Circuit Range/Performance error code? How can you fix the P0684 fault? What are the causes and symptoms of the P0684 error code?
What is the P0684? What is the Fault Code? What does it signify?
The powertrain control module P0684 will trigger if it detects an abnormal, out-of range or unreasonable voltage signal on communication circuits between the Glow Plug Control Module (GPCM), and itself. Although this code is valid only for diesel engine vehicles it does not indicate the exact fault location. This code simply indicates that there has been a fault in the system.
Note: Some V-type engines may have two glow plug controls modules. One for each bank of the cylinders. These vehicles have P0684 set. The glow plug control module for engine row 2 (which does not include Cylinder 1) should be checked.
Diesel engines use the compression stroke to ignite air-fuel mixture. However, it can be difficult to ignite the mixture when the engine is cold. All diesel engines come with glow plugs that heat the air-fuel mixture during cold temperatures.
Modern cars come with a glow-plug control module that can measure the electrical resistance of each glow plug. This module can adjust the amount of electrical current that is delivered to each glow-plug. This allows them to heat to the same temperature and in the same time. In electronic controlled systems, heating takes less than two seconds. This is in contrast to older systems that can take up to ten seconds. This allows for engine start-up at below-zero temperatures to be accelerated and extends the lifespan of components, such as glow plugs.
Modern glow plug control systems have become quite complex. While there is a control module to monitor and manage the system, it is not the only one that needs to know everything going on inside the glow plug control circuit. This allows it to effectively manage fuel delivery and other engine management strategies. The PCM monitors closely the glow plug control module as well as its associated circuits via dedicated communication circuits. The PCM will set fault code P0684 if there is a problem with communication between the PCM or the glow plug control module. This will activate the check engine light.
But, glow plugs are not required to start a hot motor. The PCM receives data from an engine coolant sensor and/or oil temperature sensor to stop glow plugs being activated when the engine is hot. To prevent premature ignition of air/fuel mixture, the PCM will disable the glow plug control system if the coolant temperature exceeds a preset limit set by the manufacturer. This can cause engine damage and possibly even burn out the glow plugs.
The P0684 fault code can affect vehicles of all makes and models, including but not limited to: Volkswagen, Mazda, Hyundai Kia, Kia, Audi or Porsche, Chevrolet, Toyota or Ford, Skoda, Skoda, Skoda, Ford, Toyota, Ford, Toyota, Ford, and Toyota.
What causes the P0684 Fault code?
Most applications have the glow plug control unit located in the engine compartment. It is usually located in the firewall. Some applications may experience failure due to excessive heat. They are located near the engine and exhaust components.
Here are some reasons why P0684 should be set.
- – Corroded, damaged, shorted, disconnected or disconnected wires and/or connections in the glow plug control device
- – Corroded, broken, or shorted connectors or wires in the harness for the CAN bus
- – Defective CAN bus circuits
- – Low battery voltage
- – Sub-industry use of low quality glow plug control module modules
- – A defective one or more glowplugs
- – Defective glow bulb solenoid valve
- – Disconnecting the glow plug control system fuse fuses
- – A defective glow plug relay
- – Engine coolant temperature sensor failure or other related sensors
- Defective glow plug control unit
- – The PCM has become faulty or requires reprogramming
What are the symptoms of the P0684 Malfunction code?
These symptoms may be present in vehicles with code P0684.
- – Make sure the engine light is on (8 drives must be repeated to cause light to fail in certain applications).
- – Difficulty starting the cold engine, especially if more that two glow plugs are faulty.
- Cold may cause engine to stall or stall.
- – Loss in power during acceleration
- – White smoke from the exhaust
- – An increase fuel consumption
- – Setting related fault codes
How do I fix the P0684 fault code?
It is possible to miss the P0684 error code, as it can be accompanied many other codes such as fuel injector codes or transmission and engine misfire codes. Avoid attempting to repair damaged parts by not diagnosing codes in their correct order. The vehicle should be tested again after any repairs.
The following repairs may be able to resolve the P0684 fault code:
- Repair of damaged, snapped, melted, or snapped wires.
- Repair of damaged CAN bus circuits
- – Replacing a dying or weak battery
- – Replacing blownfuses
- Relay for a defective glow plug
- – Replacing defective glow plugs
- – Replacing a faulty glow plug control unit
- – Check and replace, if necessary the engine coolant temperature sensor
- – Reprogramming the PCM or replacing it (rarely).
How serious is the P0684 Fault code?
The number of defective glow plugs will determine the severity of the code. The vehicle will still start if only one or two of the glow plugs is defective. You may experience a car not starting at all or running very hard when it is cold if there are more defective glow plugs. The starter motor’s life expectancy can be reduced by prolonged cranking. No matter what the fault code may be, it is important to take your vehicle to a mechanic immediately.
