What Does P0383 Mean?
The glow plug control module control circuit is reading low, indicating the signal wire from the ECM to the glow plug control module is shorted to ground or the GPCM is pulling the line low. This means the ECM cannot properly command glow plug operation. Diesel cold starting will be impaired, and the glow plug system may not activate at all or may default to a fixed timing strategy.
Common Causes
35%
Control circuit wiring shorted to ground due to chafed insulation or water intrusion
25%
Glow plug control module internal short pulling the control line low
20%
Corroded connector pins causing low-resistance path to ground
10%
ECM control circuit driver output fault
10%
Short in the CAN bus or LIN bus communication line between ECM and GPCM (on networked systems)
Diagnostic Steps
1
Disconnect the GPCM connector and measure the ECM control circuit output voltage at the GPCM harness connector. With the GPCM disconnected, the wire should read 5V or battery voltage (depending on circuit type). A 0V reading confirms a short to ground in the wiring.
2
With the GPCM still disconnected, measure resistance from the control circuit wire to ground. Reading near 0 ohms confirms a wiring short. Progressively disconnect intermediate connectors to isolate the shorted section.
3
If the wiring tests clean with the GPCM disconnected, reconnect the GPCM and re-measure. If the voltage drops to 0V, the GPCM has an internal short on the control input and must be replaced.
4
Inspect the GPCM and ECM connectors for water intrusion, corrosion, or bent/damaged pins. Clean connector terminals with electrical contact cleaner and apply dielectric grease.
5
On systems using CAN or LIN bus communication between ECM and GPCM, check bus voltages. CAN-High should read ~2.5V and CAN-Low ~2.5V with ignition on, engine off. Abnormal readings indicate a bus fault.
Estimated Repair Cost
$80 - $600
Parts + labor, varies by vehicle and location
The glow plug control module control circuit is reading low, indicating the signal wire from the ECM to the glow plug control module is shorted to ground or the GPCM is pulling the line low. This means the ECM cannot properly command glow plug operation. Diesel cold starting will be impaired, and th...
The most common cause of P0383 (Glow Plug Control Module Control Circuit Low) is: Control circuit wiring shorted to ground due to chafed insulation or water intrusion
Typical repair costs for P0383 range from $80 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Without proper glow plug control, cold starting will be significantly impaired. The vehicle is safe to drive once running. In cold climates, this could leave you stranded if the engine cannot start. Repair before exposure to cold weather conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0383 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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