P0674: Cylinder No. Glow Plug Circuit Code. 4 - Glow Plug Circuit Error Cylinder 4

Introduction

DTC P0674 is a common problem found in diesel vehicles, related to the cylinder number 4 glow plug heating circuit. This code indicates that the engine control unit (ECU) has detected a malfunction in one of the glow plug circuits, which could cause the engine to fail to start or run, especially during cold starts. Diagnosing and fixing this problem is essential to ensure proper engine operation and prevent long-term damage.

Symptoms

Symptoms of DTC code P0674 can vary depending on the condition of the vehicle and the severity of the problem. Some of the most common symptoms include:

  • Difficulty starting the engine, especially at low temperatures
  • Engine stalls or runs erratically during operation
  • Increased emission of black smoke from the exhaust
  • Engine warning light (Malfunction Indicator Lamp - MIL) comes on
  • Vibrations and abnormal noises coming from the engine

Cause

The causes of the DTC code P0674 can be different. Among the most common we find:

  • Faulty spark plug :
    The glow plug in cylinder 4 may be bad or worn, causing a malfunction in the circuit.

  • Wiring problems :
    The wires connecting the glow plug to the engine control unit may be damaged, worn or shorted, preventing the circuit from functioning properly.

  • Power problems :
    Insufficient or unstable power supply may affect the operation of the glow plug.

  • Faults in the engine control unit :
    The ECU itself may have a fault that prevents the glow plug circuit from being properly controlled.

  • Corrosion or oxidation :
    Corroded or oxidized electrical connections can cause high resistance in the circuit, compromising the function of the glow plug.

Diagnosis

Diagnosing DTC P0674 requires a systematic approach. Here are the basic steps to follow:

  1. DTC Scan :
    Use an OBD-II scanner to confirm the presence of DTC code P0674 and check for other related codes, such as P0670 (generic glow plug circuit) or P0671-P0673 (glow plug circuits for cylinders 1-3).

  2. Visual inspection :
    Check the 4 glow plug wiring and connections for signs of wear, damage, or corrosion.

  3. Checking the glow plug :
    Use a multimeter to test the resistance of the glow plug. Abnormal resistance may indicate a fault.

  4. Voltage control :
    Check that the voltage input to the glow plug is correct while the engine is running.

  5. ECU Test :
    If you suspect a fault in the engine control unit, perform a test on it to verify correct operation.

Resolution and repair

Once you have identified the causes of the problem, you can proceed with the resolution and repair. Here are some practical suggestions:

  1. Replacing the spark plug :
    If the glow plug in cylinder 4 is defective, replace it with a new one. Be sure to use a quality replacement to ensure proper operation.

  2. Wiring Repair :
    If any damage is found on the cables, repair or replace them. It is essential to ensure that all connections are tight and free from corrosion.

  3. Power Control :
    Make sure the power supply to the glow plug is stable and adequate. If there is a problem, check the fuse and electrical connections.

  4. Engine control unit diagnosis :
    If the ECU is suspected to be faulty, it may need to be repaired or replaced. This requires advanced skills and specialized equipment.

  5. Clearing DTC codes :
    After making repairs, use the OBD-II scanner to clear the DTC codes and turn the engine on to verify that the problem is resolved.

Insight into the components involved

Glow Plug Circuit Components

The glow plug ignition system is made up of several key elements that work together to ensure a smooth start of the diesel engine. The main components include:

  • Spark plug :
    An electrical device that emits heat to help ignite the fuel inside the cylinder. Each glow plug is designed to heat up quickly and maintain a suitable temperature for ignition.

  • Engine Control Unit (ECU) :
    The control unit manages the power supply and operation of the glow plugs, monitoring the engine conditions and activating them at the right time.

  • Wiring and connectors :
    These components are essential for the transmission of electrical energy from the engine control unit to the glow plugs. It is essential that they are in excellent condition to ensure proper operation.

  • Glow plug relay :
    This component controls the electrical power to the glow plugs. If the relay is faulty, the current may not reach the glow plugs, causing ignition problems.

Conclusions

DTC P0674 is a significant problem for diesel vehicles, especially during cold weather. Proper diagnosis and resolution of this problem is essential to ensure the proper functioning of the engine and prevent more serious damage. Auto mechanics must follow a methodical approach and use the right tools to identify and resolve the underlying causes. With proper maintenance and diagnosis, glow plug problems can be effectively managed, thus ensuring optimal starting and operation of the engine.

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.