What Does P066C Mean?
The PCM has detected a low voltage condition in the glow plug control circuit for cylinder 2 on a diesel engine. This indicates excessive current draw or a short to ground in the cylinder 2 glow plug circuit. The glow plug may be drawing more current than normal due to an internal short, or the wiring may be damaged. The driver may experience slightly extended cold-start cranking and some white smoke on startup, especially in cold ambient temperatures.
Common Causes
35%
Short to ground in cylinder 2 glow plug wiring
30%
Failed cylinder 2 glow plug with internal short
20%
Corroded bus bar or connector causing low-resistance path to ground
10%
Glow plug control module overcurrent on cylinder 2 driver
5%
Heat-damaged wiring insulation near exhaust manifold
Diagnostic Steps
1
Disconnect the cylinder 2 glow plug and measure its resistance — spec is typically 0.5-2.0 ohms. A reading near 0 ohms indicates an internal short.
2
With the glow plug disconnected, check for continuity from the control wire to chassis/engine ground. Continuity confirms a wiring short to ground.
3
Visually inspect the glow plug wiring and bus bar for cylinder 2 — look for heat damage, corrosion, cracked insulation, or wire-to-engine contact points.
4
If the glow plug tests good, use a clamp-on DC ammeter to measure current draw during the glow cycle. Compare to specs (typically 15-25A per plug). Excessive current confirms a short.
5
Swap the cylinder 2 glow plug with a known-good cylinder and clear codes. If the fault follows the plug, replace it. If it stays on cylinder 2, the wiring is the problem.
Estimated Repair Cost
$80 - $400
Parts + labor, varies by vehicle and location
The PCM has detected a low voltage condition in the glow plug control circuit for cylinder 2 on a diesel engine. This indicates excessive current draw or a short to ground in the cylinder 2 glow plug circuit. The glow plug may be drawing more current than normal due to an internal short, or the wiri...
The most common cause of P066C (Cylinder 2 Glow Plug Control Circuit Low) is: Short to ground in cylinder 2 glow plug wiring
Typical repair costs for P066C range from $80 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A shorted glow plug circuit can blow fuses or damage the glow plug control module if not addressed. Cold starting may be affected, and the overcurrent condition could cause wiring to overheat. Repair within a week to prevent collateral damage to the glow plug module.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P066C to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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