P0679Generic code

P0679 Code: Cylinder 9 Glow Plug Circuit

The P0679 code means the glow plug for cylinder 9, or its circuit, is not working. The diesel engine will start harder when cold and will put out white smoke for the first few minutes.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$20 to $300
Difficulty
Medium
System
Ignition and Misfires
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

On this page

What the P0679 code means

The glow plug module powers each glow plug separately and watches its current. If the plug on cylinder 9 draws no current (a burned out plug or a cut wire) or too much (a short), it tells the computer, which stores the P0679 code.

With one burned out plug the engine usually starts, but it is harder to start when cold, with white smoke and noise until it warms up. With several burned out plugs, it may not start at all in winter.

Glow plugs can break when you remove them, especially in aluminum cylinder heads. Warm up the engine, soak the plug in penetrating oil ahead of time and use the correct torque. If one breaks, there are specific extraction tools.

The manufacturer sets the numbering of cylinder 9, so confirm it in the manual before you start taking things apart.

P0679 code symptoms

  • Hard starting when cold.
  • White smoke at startup.
  • Rough idle when cold.
  • Glow plug light or check engine light on.

Likely causes of the P0679 code

  1. Burned out cylinder 9 glow plug. Infinite resistance.
  2. Loose or burned glow plug connector or wire, from engine heat.
  3. Damaged glow plug module output. Often caused by a shorted plug.
  4. Shorted glow plug. Resistance close to zero.

How to diagnose the P0679 code step by step

  1. Measure the resistance of glow plug 9. As a guide, 0.5 to 2 ohms. Infinite means it is burned out.
  2. Compare it with the other glow plugs.
  3. Check the voltage at its connector during preheat. It should be battery voltage.
  4. Check the wire and the connector.

How to fix the P0679 code

  • Replace the glow plug. It is best to replace all of them if they have high mileage.
  • Repair the connector or the wire.
  • Replace the module if its output is damaged.
  • Clear the code and verify the repair on a cold start.

Technical reference data

  • Glow plug resistance: 0.5 to 2 ohms.
  • Initial current per glow plug: 8 to 15 amps.
  • Typical tightening torque: 8 to 20 N·m (about 6 to 15 lb-ft).
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

On several popular diesels the module identifies the exact glow plug that failed, which saves time. Broken plugs in the cylinder head are a known problem on one of them.

P0679 on Volkswagen TDI

On the Volkswagen TDI the module identifies the specific glow plug.

P0679 on Ford Power Stroke 6.0 and 6.4

On the Ford Power Stroke 6.0 and 6.4 the module identifies the specific glow plug. Glow plugs that break off in the cylinder head are a known problem on the Ford Power Stroke.

P0679 on Mercedes CDI

On the Mercedes CDI the module identifies the specific glow plug.

Frequently asked questions about P0679

Can I drive with a P0679 code?
Yes. The problem is starting in the cold, not driving. Once the engine is running, it drives normally.
Should I replace just one glow plug?
If the others have high mileage, it makes sense to replace them all. A new plug next to old ones means you will likely be back for the next one soon.
Can glow plugs break when removed?
Yes, they can. Do the job with the engine warm and handle them carefully.
How much does it cost to fix P0679?
Between $20 and $300 per glow plug, including labor.
What does the P0679 code mean?
It is a generic OBD2 code that means the cylinder 9 glow plug, or its circuit, is not working.
What is the most common cause of P0679?
A burned out glow plug on cylinder 9. A loose connector or a shorted plug that damaged the module output can also set a P0679 code.

Related codes

Questions about the P0679 code

There are no questions about this code yet. Tell us about your case: vehicle, symptoms and what you have already checked.