P0384 indicates that the control circuit for Glow Plug Control Module 1 is reporting a voltage higher than expected. The engine control module detects this high voltage on the module’s driver line and sets the code, which typically points to a short to power or an internal fault in the module itself.
The driver transistor inside the module can fail shorted to the supply voltage, pulling the control line high.
A damaged or pinched wire in the control circuit may contact a constant‑voltage source, raising the signal voltage.
Poor contact can create a high‑resistance path that the ECU interprets as a high voltage condition.
A stuck‑closed relay or incorrect fuse rating can feed higher than designed voltage to the control line.
A defective driver output in the PCM is possible but rare; it should be considered only after all other causes are ruled out.
Not usually. The code most often points to a short in the glow plug control module circuit or the module itself. PCM failure is a rare cause and should be verified only after other possibilities are eliminated.
A failed glow plug typically sets a different code (e.g., P0380‑P0383). P0384 is specific to the control circuit voltage, not the plug resistance.
The vehicle may start poorly in cold weather and run rough until the engine warms. Continued operation can increase emissions and strain the starting system, so repair is recommended promptly.
Repair usually involves fixing a shorted wire or connector, replacing the glow plug control module, or correcting a faulty relay/fuse. PCM replacement is only required if diagnostics confirm a driver fault.