Code P0677 indicates that the engine control module has detected an open circuit in the glow plug heating element for cylinder 7. This means electrical current cannot flow through the plug, preventing it from heating the combustion chamber during cold starts.
The heating element inside the cylinder 7 glow plug has burnt out, creating an internal open circuit.
Corrosion or a loose fit at the glow plug terminal prevents electrical contact.
The wiring leading to cylinder 7 is chafed, broken, or shorted, interrupting the circuit.
The driver or relay within the glow plug control module has failed, preventing power from reaching the plug.
The engine computer is failing to trigger the control module or incorrectly interpreting the circuit status.
Yes, the vehicle will typically run fine once warm, but cold starting will be more difficult and may cause increased engine wear.
While not strictly necessary to clear the code, glow plugs often fail around the same time; replacing the set is common practice for long-term reliability.
No. P0677 is almost always caused by the plug itself, the wiring, or the control module. Replacing the PCM is rarely the correct solution and should only be considered after all other components are proven functional.