P0680 indicates an open (broken) electrical circuit in the glow plug for cylinder 10 of a diesel engine. Glow plugs heat the combustion chamber to assist cold starting, and this code is set when the powertrain control module (PCM) detects a loss of continuity in that specific plug's circuit. The code is most commonly seen on heavy-duty multi-cylinder diesel engines, such as those in large trucks, industrial, or stationary equipment.
The internal heating element burns out over time and creates an open circuit. This is by far the most common cause, especially in older or high-hour diesel engines.
Heat cycling, vibration, and corrosion can break the conductor or degrade the connector leading to cylinder 10, interrupting the circuit path.
The relay or solid-state controller that supplies current to the glow plugs can fail internally, leaving one or more cylinders without power.
A protective fuse or high-current link in the glow plug power supply can blow due to a short or age, cutting voltage to the entire bank or branch.
Insufficient voltage or a poor chassis ground can prevent glow plugs from reaching proper operating temperature and may set circuit codes on marginal components.
The engine control module can fail internally and falsely report an open circuit, but this is uncommon and should be considered only after every other cause has been ruled out.
Yes, in most cases the engine will run, particularly when warm. However, cold starting will be noticeably harder, the engine may run rough, and unburned fuel can wash cylinder walls or dilute the oil. It is best to repair the fault promptly.
Most often it does, but not always. The same code is set whenever the PCM sees an open circuit at cylinder 10, which can also be caused by broken wiring, a bad connector, or a failed relay/controller. Testing is required to identify the actual failed part.
No. Replacing or reprogramming the PCM is almost never the correct fix for P0680. The glow plug, its wiring, or the control relay are responsible in the vast majority of cases. Replacing the PCM without first testing the circuit is a common and expensive mistake.
If testing confirms only that one plug is open, replacing just that plug is acceptable. However, on high-hour engines the remaining glow plugs are often near the end of their service life, and many technicians recommend replacing the full set at the same time to avoid repeat labor.