Introduction

The DTC (Diagnostic Trouble Code) P0683 is a specific error that refers to the glow plug preheating system in diesel engines. When this code is detected, it means that the engine control module (ECU) has detected a malfunction in the glow plug relay circuit. Since glow plugs are essential for starting diesel engines, especially in cold conditions, troubleshooting this error is essential to ensure effective and smooth engine starting.

DTC Code P0683 Description

Code P0683: Glow Plug Preheat Relay Circuit Low

  • System involved: Ignition and preheating system, glow plugs
  • Common Symptoms: Difficulty starting engine, prolonged cranking, engine light (MIL) on, rough running of cold engine
  • Root Cause: Glow plug relay failure or a problem with the relay control circuit

How the Glow Plug System Works

Glow plugs are a vital part of diesel engines, used to preheat the air in the cylinder and aid combustion during start-up. Unlike gasoline engines, which use spark plugs to ignite the air-fuel mixture, diesel engines ignite by compressing the air. However, at low temperatures, the compressed air may not reach a high enough temperature to ignite combustion, which is where glow plugs come in.

The glow plug relay is responsible for turning the glow plug system on and off. The relay sends power to the glow plugs for the required amount of time, controlled by the ECU. A fault in the relay or associated circuit can prevent the glow plugs from working properly, leading to starting problems and the P0683 trouble code.

Causes of Code P0683

The P0683 code is triggered when the ECU detects a fault in the preheat relay circuit. This can be caused by several factors, including:

  1. Glow plug relay faulty: The relay may not be working properly, preventing the glow plugs from receiving electrical current.
  2. Faulty wires or connectors: The wiring connecting the relay to the glow plugs or ECU may be damaged or have a bad contact.
  3. Faulty Glow Plugs: If one or more of the glow plugs are faulty or burned out, the relay may not be able to send the necessary current.
  4. Faulty ECU: In some cases, the ECU may not be able to control the glow plug relay properly due to an internal malfunction.
  5. Blown Fuse: A faulty fuse in the preheat circuit could prevent power from reaching the glow plugs.

Symptoms of Code P0683

When the P0683 code occurs, you may experience a variety of symptoms that can vary in severity depending on environmental conditions and the condition of the vehicle. The most common symptoms include:

  • Difficulty starting: The diesel engine may take longer than usual to start, especially on cold days.
  • Prolonged starting: Even when the engine does start, it may take more attempts or be slower.
  • Engine Light On (MIL): The engine light comes on on the dashboard, indicating a problem with the preheat system.
  • Irregular running when cold: When the engine is cold, irregular running, such as stuttering or loss of power, may occur due to poor combustion.
  • Excessive exhaust smoke: A difficult start may cause an increase in white or gray exhaust smoke due to incomplete combustion of the fuel.

Diagnostic Procedure

To address the P0683 error code, you need to follow a structured diagnostic procedure to identify the root cause of the problem. Here are the suggested steps:

  1. Reading Trouble Codes: Use an OBD-II scanner to confirm the presence of the P0683 code and check for other associated codes, such as those related to the glow plugs or engine sensors.

  2. Visual inspection of the relay and wiring: Check the condition of the glow plug relay and electrical connectors. Inspect the wires for any signs of wear, corrosion or breakage.

  3. Glow Plug Relay Test: Using a multimeter, test the relay to ensure it is working properly. The relay should close when the ECU activates it and should supply current to the glow plugs.

  4. Checking the glow plugs: Measure the resistance of the glow plugs using a multimeter. Too high or infinite resistance indicates a burned out glow plug.

  5. Checking fuses: Check whether the fuses in the preheating circuit are blown and replace them if necessary.

  6. Checking ECU Signal: If all physical components are in good condition, it is possible that the ECU is not sending the correct signal to the glow plug relay. In this case, it may be necessary to check the ECU output with advanced diagnostic tools.

Solutions and Repairs

Once you have identified the cause of the P0683 code, there are several solutions to resolve the problem:

  1. Replacing the Glow Plug Relay: If the relay is faulty or not working properly, it must be replaced.

  2. Wiring or Connector Repair: Any damaged wiring or connectors must be repaired or replaced to ensure proper current flow to the glow plugs.

  3. Replacing Glow Plugs: If one or more glow plugs are burned out or defective, they should be replaced with new ones to ensure proper engine starting.

  4. ECU Repair or Replacement: If the ECU is unable to properly control the glow plug relay, it may need to be repaired or replaced.

  5. Replacing blown fuses: Fuses in the preheating circuit must be replaced if they are defective or blown.

Prevention

To prevent the P0683 code from recurring, it is advisable to follow some preventive practices:

  1. Regular check of glow plugs: Especially in diesel vehicles used in cold climates, it is important to periodically check the condition of the glow plugs and the preheating system.

  2. Inspecting the Relay and Wiring: Make sure the glow plug relay is working properly and that there are no problems with the electrical connections.

  3. Preventive Maintenance of the Electrical System: Regularly inspect your vehicle's electrical system to prevent problems with wiring or oxidized connectors.

Conclusions

DTC code P0683 is a clear indicator of a problem in the glow plug preheating circuit, an essential component for starting diesel engines, especially at low temperatures. Identifying and fixing this problem in a timely manner not only ensures a smooth engine start, but can also prevent further damage to the ignition system and improve the efficiency of the vehicle. By following a detailed diagnostic procedure and making the necessary repairs, you can successfully resolve the P0683 code.

Important
Not all OBD2 codes used by one manufacturer are used by other brands, and may not have the same meaning.
The information presented here is for informational purposes only. We are not responsible for any actions you take on your vehicle. If you have any concerns about repairing your vehicle, please contact your repair shop.