What Does P068F Mean?
The PCM has detected a high voltage condition on the cylinder 8 glow plug control circuit, indicating an open circuit or very high resistance in the glow plug or its wiring. Cylinder 8 is not receiving proper pre-heat for cold starting. The driver may experience extended cranking, rough cold idle, and white exhaust smoke, particularly in cold weather.
Common Causes
40%
Cylinder 8 glow plug element burned open
25%
Open circuit in the wiring from GPCM to cylinder 8
20%
Corroded or loose connector at the cylinder 8 glow plug
10%
GPCM output open for cylinder 8 channel
5%
Ground path issue for glow plug bank
Diagnostic Steps
1
Measure cylinder 8 glow plug resistance; OL reading confirms the heating element has failed open. Spec is typically 0.3-2.0 ohms.
2
Verify continuity from the GPCM output terminal to the cylinder 8 glow plug connector; an open confirms a harness or bus bar break.
3
Inspect the bus bar at cylinder 8 (often the last cylinder on V8 engines) for corrosion, loose nuts, or cracked sections.
4
Command GPCM activation and measure voltage at the cylinder 8 harness connector; battery voltage should be present.
5
If the glow plug needs replacement and is seized, use a specialized glow plug removal tool and apply heat to the surrounding cylinder head material to aid extraction.
Estimated Repair Cost
$75 - $500
Parts + labor, varies by vehicle and location
The PCM has detected a high voltage condition on the cylinder 8 glow plug control circuit, indicating an open circuit or very high resistance in the glow plug or its wiring. Cylinder 8 is not receiving proper pre-heat for cold starting. The driver may experience extended cranking, rough cold idle, a...
The most common cause of P068F (Cylinder 8 Glow Plug Control Circuit High) is: Cylinder 8 glow plug element burned open
Typical repair costs for P068F range from $75 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive once the engine reaches operating temperature. On a V8 diesel, one non-functional glow plug reduces cold-start reliability but is not catastrophic. Repair before winter to ensure reliable starting.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P068F 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
OBD2 Scanner
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