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Technical Description of OBD-II Trouble Code
Communication Circuit between Glow Plug Control Module and PCM
What does that mean?
This generic powertrain code (DTC) applies to all vehicle makes and models (1996-newer). However, the specific repair steps may vary slightly depending on the model.
Code P0683 indicates a loss of communication between the Glow Plug Control Module and PCM. This fault prevents the PCM from sending commands to the glow plug control module, which is responsible for turning the glow plugs on and off.
The code does not pinpoint a specific part within the system, only the area of failure. The glow plug circuit is relatively simple and can be diagnosed and repaired with basic knowledge of using a volt/ohmmeter.
What is the purpose of the glow plugs?
To understand their function, you need to grasp the operating principles of a diesel engine.
Unlike gasoline engines that require a spark to ignite the fuel, diesel engines rely on high compression. The compressed air generates extreme heat, which ignites the fuel.
When a diesel engine is cold, it is challenging to generate enough heat through compression to ignite the fuel. The cold engine block cools the air, causing a slower increase in temperature that is insufficient for starting.
When the PCM detects that the engine is cold based on signals from the oil and transmission temperature sensors, it activates the glow plugs. The glow plugs heat up and transfer heat to the combustion chamber, aiding in engine startup. They operate on a timer and only remain active for a few seconds to prevent burnout.
How do they operate?
When the PCM senses a cold engine, it grounds the Glow Plug Control Module (GPCM). The GPCM then grounds the glow plug solenoid, which is similar to a starter solenoid, on the valve cover.
The solenoid sends power to a glow plug bus bar, which has a separate wire for each glow plug. Power travels to the glow plugs, where they heat up the cylinders to facilitate startup.
The GPCM is a timer and remains activated for a short period. This duration is sufficient to start the engine while protecting the glow plugs from overheating.
Symptoms
Symptoms of a P0683 code may include:
Potential Causes
Possible causes for this DTC may include:
Diagnostic & Repair Steps
Based on my experience, this is a common problem with diesel engines regardless of the manufacturer. Due to the high amperage required for the glow plugs and their tendency to burn out, I recommend starting with the most common issues.
The GPCM typically uses low amperage and is unlikely to fail. The solenoid is also rarely replaced. When dealing with high amperage, even a slight looseness in a connection can cause an arc and damage the connector.
If the above steps do not identify the problem, consult a service manual and refer to the page depicting the glow plug circuit. Look for the color and pin number for power to the GPCM and power from the GPCM to the solenoid. Use a voltmeter to probe these terminals as directed.
If there is no power to the GPCM, the PCM has failed. If there is voltage to the GPCM but no voltage to the solenoid, replace the GPCM.
Professional Service
We always recommend seeking professional mechanical assistance to resolve this issue. However, if that is not possible, we offer the option to permanently delete this specific DTC while keeping all other codes active. If you are interested in this service, please upload your ECU file to our portal.
