P0673 indicates the Powertrain Control Module (PCM) has detected an open circuit in the glow plug system for cylinder 3. The glow plug circuit is not providing the expected resistance, meaning the circuit is broken and the glow plug is not functioning. This code is specific to diesel engines that use glow plugs for cold starting.
The glow plug element itself has burned out or broken, creating an open circuit with infinite resistance.
The wiring harness to cylinder 3 glow plug is broken, frayed, or the connector is corroded, loose, or disconnected.
The relay that energizes the glow plugs has failed, or the integral glow plug module for that cylinder is defective.
The fuse protecting the glow plug circuit has failed due to overload or short circuit.
The ground path for the glow plug circuit is compromised due to corrosion, loose bolt, or damaged ground strap.
The control module itself has failed, though this is an uncommon cause and should be diagnosed only after all other possibilities are ruled out.
Yes, the vehicle can typically be driven, but cold starting will be difficult and the engine may run roughly and produce white smoke until it warms up. In warm weather or mild climates, symptoms may be barely noticeable.
Not necessarily, but it is common for glow plugs to fail in pairs. Many technicians recommend replacing all glow plugs at once if one fails, as the others are likely near end of life and will likely fail soon.
No. While the PCM monitors the glow plug circuit and sets the code when it detects an open, the PCM itself is very rarely the cause of P0673. The failed component (glow plug, wiring, relay) is almost always to blame. Replacing the PCM for this code is usually unnecessary and costly.
A basic digital multimeter is sufficient to check glow plug resistance and circuit voltage. A visual inspection requires no tools at all. Advanced diagnostics may require a scan tool, but many auto parts stores will read codes for free.