The P0670 code indicates that the powertrain control module (PCM) has detected an open circuit or malfunction in the control circuit of the glow plug control module. This module manages the operation of the glow plugs, which are essential for cold starting in diesel engines. When the circuit is open, the glow plugs may not function, leading to hard starting or a no-start condition in cold weather.
The control module itself may have failed internally due to age, heat, or electrical overload, preventing proper operation of the glow plugs.
Damaged, corroded, or broken wires between the PCM and the glow plug control module can cause an open circuit, interrupting communication or power.
A blown fuse or defective relay in the glow plug circuit can cut power to the control module, triggering the code.
One or more failed glow plugs can draw too much current, damaging the control module or causing the circuit to open.
Poor connections at the glow plug control module or related harness connectors can create high resistance or an open circuit.
In very rare cases, the powertrain control module itself may be faulty, but this should only be considered after all other possibilities are ruled out.
You may be able to drive, but cold starts will be difficult and could cause engine misfires, increased emissions, and potential damage from unburned fuel. It is best to address the issue promptly.
Replacing the module may fix the code, but you should first check the wiring, connectors, and glow plugs themselves. A faulty glow plug can overload and damage a new module, leading to repeat failure.
No, the PCM is very rarely the cause. The problem is almost always with the glow plug control module, wiring, fuses, or glow plugs. Replacing the PCM without proper diagnosis is a costly mistake.
Ignoring the code can lead to hard starting, especially in cold weather, increased engine wear from unburned fuel washing cylinder walls, and potential damage to the catalytic converter or diesel particulate filter.