What Does P06C8 Mean?
The ECM has detected that the cylinder 4 glow plug is not operating correctly in this diesel engine. The glow plug's current draw, resistance, or temperature feedback is outside the expected range. Symptoms typically include difficult cold starting, rough running for the first 30–60 seconds after startup, white exhaust smoke during warm-up, and possible increased emissions.
Common Causes
45%
Failed or degraded cylinder 4 glow plug (open element, excessive resistance, or tip damage)
20%
Damaged wiring or corroded connector to the cylinder 4 glow plug
15%
Glow plug control module (GPCM) output failure for cylinder 4 channel
12%
Poor engine ground causing high resistance in the glow plug return circuit
8%
ECM glow plug monitoring circuit internal error
Diagnostic Steps
1
Disconnect the cylinder 4 glow plug and measure its resistance — expect 0.5–2.0 ohms. Replace if open or above 6 ohms.
2
Verify battery voltage at the harness connector to cylinder 4 during the glow preheat cycle (key ON, engine cold). No voltage indicates wiring or GPCM fault.
3
Inspect the cylinder 4 glow plug wiring for chafing against engine components, heat shield damage, or connector corrosion.
4
Use a clamp ammeter to measure real-time current draw on the cylinder 4 circuit during the glow cycle and compare against a known-good cylinder — they should match within 10%.
5
If replacing the glow plug, check the glow plug bore for carbon buildup or thread damage that could affect the new plug's ground path and seating.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The ECM has detected that the cylinder 4 glow plug is not operating correctly in this diesel engine. The glow plug's current draw, resistance, or temperature feedback is outside the expected range. Symptoms typically include difficult cold starting, rough running for the first 30–60 seconds after st...
The most common cause of P06C8 (Cylinder 4 Glow Plug Incorrect) is: Failed or degraded cylinder 4 glow plug (open element, excessive resistance, or tip damage)
Typical repair costs for P06C8 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to drive, especially in warm weather. Cold starting may require extended cranking. If this code appears alongside other cylinder glow plug codes, cold-start reliability is significantly compromised. Prolonged operation with failed glow plugs can accelerate DPF soot loading and trigger regeneration issues.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P06C8 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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