What Does P06C5 Mean?
The ECM has detected that the glow plug in cylinder 1 is not functioning correctly on this diesel engine. Glow plugs preheat the combustion chamber to assist cold starting and reduce emissions during warm-up. The driver may notice hard starting in cold weather, rough idle for the first few minutes after starting, white smoke from the exhaust during warm-up, and potentially a check engine light.
Common Causes
45%
Failed or degraded glow plug in cylinder 1 (open circuit, high resistance, or carbon buildup)
20%
Wiring harness fault — corroded, chafed, or broken wire to cylinder 1 glow plug
15%
Faulty glow plug control module (GPCM) not delivering correct voltage/duration
12%
Poor ground connection at the glow plug or engine block ground strap
8%
ECM internal fault in the glow plug monitoring circuit
Diagnostic Steps
1
Measure glow plug resistance with the connector disconnected — a healthy glow plug typically reads 0.5–2.0 ohms. An open circuit or reading above 6 ohms indicates a failed plug.
2
With the glow plug harness disconnected, check for battery voltage at the harness connector when the glow plug cycle is commanded on (key ON, engine cold). No voltage points to a wiring or GPCM issue.
3
Inspect the wiring harness and connector to the cylinder 1 glow plug for corrosion, heat damage, or broken pins. Diesel engine bays run hot and vibrate heavily.
4
Monitor glow plug current draw using a clamp ammeter during the preheat cycle — each plug should draw 15–25 amps initially, tapering to 8–12 amps. Compare cylinder 1 to a known-good cylinder.
5
If the glow plug and wiring test good, check the glow plug control module output with a multimeter or oscilloscope to verify proper PWM signal and duration for cylinder 1.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The ECM has detected that the glow plug in cylinder 1 is not functioning correctly on this diesel engine. Glow plugs preheat the combustion chamber to assist cold starting and reduce emissions during warm-up. The driver may notice hard starting in cold weather, rough idle for the first few minutes a...
The most common cause of P06C5 (Cylinder 1 Glow Plug Incorrect) is: Failed or degraded glow plug in cylinder 1 (open circuit, high resistance, or carbon buildup)
Typical repair costs for P06C5 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle is generally safe to drive, but cold starting will be increasingly difficult, especially in temperatures below 40°F. Extended cranking can stress the starter and battery. Incomplete combustion during warm-up increases emissions and can lead to cylinder wash and accelerated engine wear over time.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P06C5 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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