Cylinder 9 Glow Plug Circuit Malfunction
The P0679 code indicates a fault in the glow plug circuit for cylinder 9. Glow plugs are used in diesel engines to preheat the combustion chamber for cold starts. This code is triggered when the Engine Control Module (ECM) detects an open or short circuit in the glow plug or its wiring, or when the glow plug resistance is out of specification. This can lead to hard starting, misfires, and increased emissions, especially in cold weather.
01. Most Common Causes
- Faulty glow plug in cylinder 9
- Open or short in glow plug wiring or connector
- Failed glow plug relay or fuse
- ECM issue (rare)
02. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Engine misfire or rough idle
- Check Engine Light illuminated
- Excessive smoke on startup
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect glow plug wiring and connector for cylinder 9 for damage or corrosion.
Step 3: Measure resistance of glow plug 9; should be low (0.5-2 ohms). Replace if open or high resistance.
Step 4: Check glow plug relay and fuse operation.
Step 5: If all else is fine, test ECM output to glow plug circuit.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive, but starting may be difficult in cold weather, and the engine may run rough. It's best to repair promptly to avoid further issues.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on glow plug accessibility and shop rates.