In gasoline engines, spark plugs burn the fuel. In the case of diesel engines, although they do not use spark plugs because the fuel is burned by compression, they have glow plugs that play a very important role in a cold climate.
These glow plugs not only increase the temperature of the diesel engine during cold weather or after long periods of engine inactivity but also reduce engine emissions. The glow plugs heat the cylinder head for a few seconds to bring the engine to normal operating temperature.
When a malfunction occurs in the number 4 glow plug circuit, the DTC P0674 OBD2 code is set because the PCM (Powertrain Control Module) has observed that the reference voltage of this glow plug circuit has varied at least 10% over the manufacturer’s specifications.