What Does P068C Mean?
The PCM has detected a low voltage condition on the cylinder 7 glow plug control circuit. The circuit is reading lower than expected, suggesting a short to ground in the glow plug element or its wiring. Cylinder 7 may not receive proper pre-heat during cold starts, and the driver may notice extended cranking, rough idle, and white smoke during cold operation.
Common Causes
40%
Cylinder 7 glow plug internally shorted to ground
25%
Short to ground in the wiring from GPCM to cylinder 7
20%
Glow plug control module output driver shorted
10%
Moisture or corrosion at the cylinder 7 glow plug connector
5%
PCM signal circuit fault for glow plug monitoring
Diagnostic Steps
1
Measure cylinder 7 glow plug resistance with a multimeter; spec is typically 0.3-2.0 ohms. A near-zero reading confirms an internal short.
2
Disconnect the glow plug and measure the harness wire for resistance to ground; it should read OL. A low reading indicates a wiring short.
3
Inspect the wiring along the engine block to cylinder 7 for heat damage, chafing, or pinched wires, especially near exhaust manifold routing.
4
With the plug disconnected, command GPCM activation and verify battery voltage at the GPCM output connector for the cylinder 7 channel.
5
Use a current clamp on the cylinder 7 feed wire during activation to measure actual current draw; compare to manufacturer specification (typically 15-25A per plug).
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
The PCM has detected a low voltage condition on the cylinder 7 glow plug control circuit. The circuit is reading lower than expected, suggesting a short to ground in the glow plug element or its wiring. Cylinder 7 may not receive proper pre-heat during cold starts, and the driver may notice extended...
The most common cause of P068C (Cylinder 7 Glow Plug Control Circuit Low) is: Cylinder 7 glow plug internally shorted to ground
Typical repair costs for P068C range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive once the engine is running and warm. A shorted glow plug drawing excessive current could blow the glow plug fuse or damage the GPCM, which would then affect all cylinders. Repair before cold weather.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P068C 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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