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P0384 OBD-II Trouble Code: Glow Plug Control Module Control Circuit High

check engine light

P0384 code definition

The P0384 code is stored when the PCM detects a malfunction in the voltage reading of the glow plug heater circuit – specifically, a reading that is too high. This will often be accompanied by other glow plug circuit codes.

What the P0384 code means

The glow plug system provides the heat that the engine needs to begin combustion in cold temperatures. Glow plugs heat before, during, and after cranking, and the temperature and voltage of the glow plugs is monitored by the ECM. If the voltage reading detected by the ECM is more than 10% higher than the reading recommended by the manufacturer, the PCM will store the P0384 code.

What causes the P0384 code?

Most of the time, a faulty glow plug is to blame for the P0384 code. However, there could be quite a few other causes, including:

  • Faulty glow plug relay
  • Bad glow plug module or timer
  • Loose, corroded, or shorted glow plug circuit electrical connectors
  • Loose, shorted, or open wiring in the glow plug heater circuit
  • Blown fuses, which also indicate an underlying issue elsewhere
  • Open or shorted glow plug harness

What are the symptoms of the P0384 code?

Most vehicle owners will observe a slow start, and possibly even white smoke from the exhaust when the vehicle does start. The engine may be exceedingly loud, and the glow plug indicator lamp may stay on constantly. The code will be stored in the PCM, and the Check Engine lamp will illuminate.

How does a mechanic diagnose the P0384 code?

After an OBD-II scanner detects the P0384 code, a technician should begin with a visual inspection of all the wiring and connectors related to the glow plug heater circuit. Any damaged elements should be replaced, reconnected, or repaired as necessary. They should then clear the code and perform a test drive, checking that the Check Engine light does not reappear.

If the light does reappear, the mechanic can then move on to checking each of the individual glow plug connectors for the proper voltage and ground signals. As the mechanic moves through each potential repair to find the issue, they should be sure to clear the code from the PCM and retest the system after each step. This will ensure that they do not waste time or money repairing things when the issue has already been fixed.

Common mistakes when diagnosing the P0384 code

Most often, the wiring, connectors, and/or the glow plug itself are to blame. However, many technicians report that the glow plug timers and glow plug relays are often replaced when they don’t need to be. Mechanics should be sure to check wiring and commonly at-fault parts before replacing anything.

How serious is the P0384 code?

If the P0384 code is stored in the PCM, the vehicle should be repaired right away – especially if the weather is cold. This issue can cause major issues with the start up and operation of a vehicle.

What repairs can fix the P0384 code?

There are many ways that a technician can address a P0384 code detection. They include:

  • Replacing a faulty glow plug
  • Replacing a faulty glow plug relay
  • Replacing a bad glow plug module or timer
  • Repairing loose, corroded, or shorted glow plug circuit electrical connectors
  • Repairing loose, shorted, or open wiring in the glow plug heater circuit
  • Replacing blown fuses, and searching for and repairing the underlying issue that a blown fuse can indicate
  • Repairing an open or shorted glow plug harness

Additional comments for consideration regarding the P0384 code

While attempting to diagnose and repair the issue behind the P0384 code, it is important to be careful and wear the proper safety gear. Glow plugs get very hot very quickly; within a few seconds, a properly-functioning glow plug will be orange from the heat.

Need help with a P0384 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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