What Does P0680 Mean?
The PCM has detected a malfunction in the glow plug circuit for cylinder 10. This code is specific to large diesel engines with 10 or more cylinders, such as heavy-duty commercial trucks or industrial equipment. The affected cylinder may not receive adequate preheat, causing cold-start difficulties and rough running until the engine is warm.
Common Causes
40%
Failed cylinder 10 glow plug (open or shorted element)
25%
Wiring fault in harness to cylinder 10 glow plug
20%
Glow plug control module fault on cylinder 10 output
10%
Corroded connector or bus bar at cylinder 10 location
5%
Poor ground connection for the bank containing cylinder 10
Diagnostic Steps
1
Measure resistance of the cylinder 10 glow plug; typical spec is 0.3-1.5 ohms for heavy-duty applications. OL indicates open, near 0 indicates short.
2
Check for voltage at the cylinder 10 glow plug connector while commanding glow plug activation; battery voltage should be present during the glow cycle.
3
Inspect the lengthy wiring run to cylinder 10 for chafing, heat damage, or loose connections, paying attention to areas near exhaust components and turbocharger plumbing.
4
Verify the glow plug control module is commanding proper voltage and duration to the cylinder 10 output by monitoring with a graphing multimeter or oscilloscope.
5
Check the engine ground straps for the cylinder bank containing cylinder 10; heavy-duty engines often have multiple ground points that can corrode.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The PCM has detected a malfunction in the glow plug circuit for cylinder 10. This code is specific to large diesel engines with 10 or more cylinders, such as heavy-duty commercial trucks or industrial equipment. The affected cylinder may not receive adequate preheat, causing cold-start difficulties ...
The most common cause of P0680 (Cylinder 10 Glow Plug Circuit) is: Failed cylinder 10 glow plug (open or shorted element)
Typical repair costs for P0680 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The engine should still run once started, but one failed glow plug on a large diesel can cause that cylinder to misfire during cold operation. On commercial vehicles, this can reduce power output. Safe to continue driving but should be repaired to maintain cold-start reliability and emissions compliance.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0680 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Cold Start / Glow Plug System
Difficulty
Type
Generic (SAE)
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