P0684 OBD-II: Glow Plug Control Module to PCM Communication Circuit
P0684 Severity
Should you fix P0684 yourself?
Identifying an OBD code is just the start of a complete diagnostic routine. Most trouble codes are caused by a sensor reporting a value that is out of range. Just replacing a sensor may not fix underlying issues. Be sure to understand the code, the part or system in your car that the code refers to, and the risks of delaying professional repair.
Proper diagnosis will save you time and money on unnecessary repairs.
Urgent codes indicate immediate action is necessary. These are urgent and significant malfunctions that can cause severe damage to the vehicle or harm the driver and passengers.
What causes OBD-II fault code P0684?
The Glow Plug Module controls the glow plugs used on diesel engines to preheat the cylinder before the engine is started. If the engine control module (PCM) cannot communicate with the Glow Plug Module, the PCM will set code P0684.
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OBD II Fault Code
- OBD II P0684
OBD-II Code Hard or no start in cold weather is defined as a Glow Plug Control Module to PCM Communication Circuit
The Glow Plug Module controls the glow plugs used on diesel engines to preheat the cylinder before the engine is started. If the engine control module (PCM) cannot communicate with the Glow Plug Module, the PCM will set code P0684.
Hard or no start in cold weather Symptoms
- Engine may not start
- Hard or no start in cold weather
Common Problems That Trigger the P0684 Code
- Glow plug control module failure
- Powertrain Control Module (PCM) failure
- Wiring issue
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