Glow Plug Circuit Malfunction Cylinder 1 (Volkswagen)
What does P1679 mean?
The P1679 code means the vehicle's onboard diagnostic system has detected: Glow Plug Circuit Malfunction Cylinder 1 (Volkswagen). This is a moderate severity code.
Common Symptoms
- Hard starting in cold weather
- Glow plug warning light stays on or flashes
- White smoke on cold start
- Check Engine Light on
- Rough idle when cold
Probable Causes (Ranked by Likelihood)
- Burned out glow plug in cylinder 1 Very High
- Faulty glow plug control module High
- Corroded glow plug connector or wiring Moderate
- Damaged glow plug bus bar Low
Step-by-Step Diagnostic Procedure
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Measure resistance of the cylinder 1 glow plug (typical spec is 0.5-2.0 ohms). An open reading means the plug is burned out.
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Check the glow plug connector for corrosion and tight fit.
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Measure voltage at the glow plug connector during glow cycle (should be battery voltage for specified time).
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Test the glow plug control module output to each cylinder.
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If the plug is seized, apply penetrating oil and use a specialized glow plug removal tool to avoid breaking it.
Frequently Asked Questions
Can I drive with a bad glow plug?
Yes, once the engine is warm. However, cold starts will be difficult and you may experience rough running for the first minute.
Should I replace all glow plugs at once?
It is recommended. If one has failed, the others are likely near the end of their life. Replacing all four prevents repeated repairs.
Why do glow plugs break during removal?
Carbon buildup around the glow plug tip can seize it in the cylinder head. Using penetrating oil and a torque-controlled removal tool reduces breakage risk.