The P0674 code indicates that the powertrain control module (PCM) has detected an open circuit in the glow plug circuit for cylinder 4. This means the circuit that supplies power to the glow plug is incomplete, preventing proper heating of the diesel fuel.
The glow plug itself may have an internal open circuit, preventing it from heating.
A broken, corroded, or loose wire or connector in the cylinder 4 glow plug circuit can cause an open circuit.
If the fuse or fusible link that protects the glow plug circuit is blown, the circuit will be open.
The relay or control module that energizes the glow plugs may have a fault, though this is less common.
The engine control unit could have an internal failure preventing it from driving the circuit, but this is the least likely cause.
No. In the vast majority of cases the problem is a failed glow plug, wiring issue, or blown fuse. PCM failure is extremely rare.
You may be able to drive, but expect hard starting and increased emissions, especially in cold weather. The fault should be repaired promptly to avoid damage to the exhaust system.
If the glow plug is the cause, replacing it will fix the code, but the underlying wiring or connector issue must also be addressed if present.
It is moderately urgent because a malfunctioning glow plug can lead to poor starting, increased fuel consumption, and higher emissions. Addressing it soon prevents further issues.