What Does P0384 Mean?
The glow plug control module control circuit is reading high, meaning the signal wire from the ECM to the GPCM is stuck at a high voltage level. This could indicate an open circuit, a short to battery voltage, or a GPCM fault. The ECM cannot modulate glow plug operation properly, which may cause the glow plugs to stay on too long (risking damage) or not activate at all, depending on the system's failsafe strategy.
Common Causes
35%
Open circuit in the control wire between ECM and GPCM due to a broken wire or disconnected connector
25%
Control circuit wire shorted to battery voltage (B+) from contact with a power wire
20%
Glow plug control module not responding to ECM commands (internal fault)
10%
Corroded or backed-out connector pin causing an open in the control circuit
10%
ECM pull-up resistor or driver circuit fault holding the line high
Diagnostic Steps
1
Measure the control circuit voltage at the GPCM connector with the ignition on. Compare to expected operating voltages: during glow activation the line should toggle between high and low states. A fixed high voltage confirms the fault.
2
Disconnect the GPCM and check if the control line voltage drops to the expected idle state. If it remains high with GPCM disconnected, the wire is shorted to B+ or the ECM driver is faulty.
3
Check for continuity of the control wire from ECM to GPCM. An open reading (OL) with both ends disconnected confirms a broken wire. Inspect the full wire route for damage.
4
Verify the GPCM has a solid ground connection. A poor ground can cause the control circuit to float high. Measure ground resistance from the GPCM ground pin to battery negative (should be <0.5 ohms).
5
If wiring is intact, test the GPCM by substituting a known-good module. If the code clears, the original GPCM is faulty. If the code persists, focus on the ECM driver circuit.
Estimated Repair Cost
$80 - $650
Parts + labor, varies by vehicle and location
The glow plug control module control circuit is reading high, meaning the signal wire from the ECM to the GPCM is stuck at a high voltage level. This could indicate an open circuit, a short to battery voltage, or a GPCM fault. The ECM cannot modulate glow plug operation properly, which may cause the...
The most common cause of P0384 (Glow Plug Control Module Control Circuit High) is: Open circuit in the control wire between ECM and GPCM due to a broken wire or disconnected connector
Typical repair costs for P0384 range from $80 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If the circuit is stuck high and glow plugs stay energized continuously, they can overheat and crack glow plug tips, which can fall into the combustion chamber and cause severe engine damage. If the glow plug indicator light stays on continuously, turn off the engine and have it towed. If glow plugs are not activating, cold starting is impaired but there is no damage risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0384 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug / Cold Start System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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