What Does P0682 Mean?
The PCM has detected a malfunction in the glow plug circuit for cylinder 12. This code is found on very large diesel engines with 12 cylinders, commonly V12 configurations in heavy-duty trucks and industrial equipment. The cylinder 12 glow plug is not operating correctly, compromising cold-start ability for that cylinder.
Common Causes
40%
Failed cylinder 12 glow plug element
25%
Wiring harness fault to cylinder 12 (open, short, or high resistance)
20%
Glow plug control module output driver failure for cylinder 12
10%
Corroded connector at the remote cylinder 12 location
5%
Engine ground issue affecting rear bank
Diagnostic Steps
1
Measure cylinder 12 glow plug resistance; compare to the manufacturer specification (typically 0.3-1.5 ohms). An open or shorted reading confirms plug failure.
2
Check for proper voltage at the cylinder 12 connector during GPCM-commanded activation; battery voltage should be present for the programmed duration.
3
Inspect the full length of the wiring run to cylinder 12 (the longest run in a V12), paying special attention to areas near heat sources and vibration contact points.
4
Verify the ground return path for the bank including cylinder 12 by performing a voltage drop test on the ground circuit while the glow plug is activated.
5
If the glow plug tests bad, attempt removal carefully; cylinder 12 plugs on large engines are often in tight spaces and prone to seizing in the head.
Estimated Repair Cost
$100 - $700
Parts + labor, varies by vehicle and location
The PCM has detected a malfunction in the glow plug circuit for cylinder 12. This code is found on very large diesel engines with 12 cylinders, commonly V12 configurations in heavy-duty trucks and industrial equipment. The cylinder 12 glow plug is not operating correctly, compromising cold-start abi...
The most common cause of P0682 (Cylinder 12 Glow Plug Circuit) is: Failed cylinder 12 glow plug element
Typical repair costs for P0682 range from $100 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The engine is safe to operate once warmed up. On a 12-cylinder engine, one failed glow plug has minimal impact on running performance, but cold starting in extreme temperatures may be affected. Repair at the next scheduled maintenance interval.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0682 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Cold Start / Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
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