P0679 Fault Code

P0679 OBD-II Trouble Code Short Description

Cylinder 9 Glow Plug Circuit

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What does trouble code P0679 mean?

The P0679 fault code indicates a problem with the glow plug circuit for cylinder 9. This typically relates to the engine's pre-heating process which ensures optimal combustion during cold starts, particularly in diesel engines. In this scenario, the glow plug may be malfunctioning, the circuit could be open or shorted, or there may be issues with the glow plug control module itself.

  • Glow plugs help heat the air in the combustion chamber before starting.
  • A malfunctioning glow plug can lead to hard starting, especially in low temperatures.
  • Diagnostic procedures often involve checking the resistance of the glow plug and the integrity of the circuit.

Symptoms

What are the symptoms of the P0679 code?

Drivers may experience a variety of symptoms if the P0679 code is present:

  • Difficulty starting the engine, particularly in cold weather.
  • Increased white smoke coming from the exhaust during initial start-up.
  • Rough idling or misfiring of the engine until it reaches optimal operating temperature.
  • Poor fuel economy due to incomplete combustion during the start-up phase.

Causes

What causes the P0679 code?

Several factors can contribute to the activation of the P0679 code:

  • A defective glow plug in cylinder 9 that is either burnt out or shorted.
  • Wiring issues such as short circuits, corroded connections, or open circuits in the glow plug circuit.
  • A failing glow plug relay that does not supply power to the glow plug as needed.
  • Problems within the engine control module (ECM) or the glow plug control module affecting the operation of the glow plug.

Possible Solutions

How to fix P0679?

To resolve the P0679 fault code, it's essential to follow a systematic approach:

  • Start by scanning the vehicle with an OBD-II scanner to confirm the fault code and check for any additional codes.
  • Inspect the glow plug for cylinder 9, checking for physical damage and testing it with a multimeter for proper resistance.
  • Check the wiring harness and connectors for any signs of damage, corrosion, or loose connections.
  • Test the glow plug relay and replace if necessary.
  • If all components are functioning correctly, consider checking the ECM or glow plug control module for faults.
P0679 Cylinder 9 Glow Plug Circuit