What Does P0677 Mean?
The PCM has detected a malfunction in the cylinder 7 glow plug circuit on a diesel engine. This applies to V8 or larger diesel engines. The glow plug or wiring for cylinder 7 is not operating within expected parameters. On V8 diesels, cylinder 7 is typically on bank 2 (passenger side). Without proper pre-heating, this cylinder will not fire cleanly during cold starts, contributing to harder starting and white exhaust smoke.
Common Causes
40%
Failed cylinder 7 glow plug (burned out or degraded)
25%
Corroded or loose connection at cylinder 7 glow plug
20%
Wiring fault in the cylinder 7 glow plug circuit
10%
Glow plug control module output failure for cylinder 7
5%
Glow plug tip broken inside combustion chamber
Diagnostic Steps
1
Measure cylinder 7 glow plug resistance with the connector removed — spec is 0.5-2.0 ohms. Compare to all other cylinders.
2
On V8 diesel applications (e.g., Ford 6.0L/6.7L Power Stroke, GM Duramax), cylinder 7 access varies. Identify the correct cylinder and locate the bus bar connection.
3
Verify glow plug module output for cylinder 7 by measuring voltage at the bus bar during the glow cycle (key on, engine off). Expected: battery voltage for the glow timer duration.
4
Inspect the complete bus bar for bank 2 — check for cracks, loose connections, and corrosion at all contact points. A single bad connection can affect downstream plugs.
5
If the glow plug is seized, do not use excessive force. Apply penetrating oil, warm the engine, and use a proper glow plug extraction tool. On some V8 diesels (e.g., Ford 6.0L), glow plug extraction is a known difficult procedure requiring special tooling.
Estimated Repair Cost
$80 - $600
Parts + labor, varies by vehicle and location
The PCM has detected a malfunction in the cylinder 7 glow plug circuit on a diesel engine. This applies to V8 or larger diesel engines. The glow plug or wiring for cylinder 7 is not operating within expected parameters. On V8 diesels, cylinder 7 is typically on bank 2 (passenger side). Without prope...
The most common cause of P0677 (Cylinder 7 Glow Plug Circuit) is: Failed cylinder 7 glow plug (burned out or degraded)
Typical repair costs for P0677 range from $80 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
On a V8 diesel, one failed glow plug has relatively minor cold-start impact. However, V8 diesels are often in heavy-duty trucks where reliable cold starting is essential. If multiple glow plugs are failing, starting in cold weather can be severely compromised. Address before cold conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0677 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
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