P0674: Glow Plug Circuit Fault, Cylinder 4 (Solution)

P0674 is the cylinder-4-specific counterpart to P0671/P0672/P0673 and describes an electrical fault in the ignition coil circuit for cylinder 4 (Q13). In most cases, the cause is either the spark plug itself or its wiring, and less frequently, the engine control unit.


What does P0674 mean?
The engine control unit monitors the circuit of each glow plug individually. If there is an electrical fault in the glow plug circuit for cylinder 4 (Q13), code P0674 is set. The pre-glow function for this cylinder is disabled, which results in poorer cold starting performance. The code is cylinder-specific and only indicates that the circuit is faulty; it does not specify whether the fault is caused by the glow plug or the wiring, and further inspection is required to determine the cause.


Typical symptoms:
- No preheating phase (for the affected cylinder).
- Poor cold start.
- Engine check light is on.
- Rough engine running immediately after starting.


Most common causes:
- Spark plug, cylinder 4, defective (most common cause).
- Spark plug wiring for cylinder 4 is faulty.
- Loose connection/faulty connector at the glow plug.
- Interruption in the glow plug circuit of the cylinder.


Diagnosis with VCDS:
- Autoscan: P0674 code found in the engine control unit (01 - Engine).
- Individually test each glow plug for cylinder 4 (a break in the circuit indicates a defect).
- Check the wiring and connector for the glow plug, cylinder 4.
- Measure the resistance of the spark plugs in the other cylinders for comparison.
- After repair, clear the error memory and check cold start performance.

"Measuring resistance with a multimeter can sometimes be unreliable because a certain amount of current needs to flow. It's better to use a 55W incandescent light bulb connected in series to determine if current is flowing through the heating element."