P0381 OBD-II Trouble Code: Glow Plug/Heater Indicator Circuit Malfunction

P0381 code definition

The P0381 code represents a problem with the glow plug or heater indicator circuit. In some vehicles, this code is sometimes also referred to as the “wait to start lamp control circuit.” The code is often accompanied by other glow plug circuit codes, such as P0380, which indicates a malfunction in heater circuit A, or P0382, which specifies heater circuit B.

What the P0381 code means

P0381 is the OBD-II generic code for a glow plug/heater indicator circuit malfunction. The glow plug system, found in diesel vehicles, helps to provide heat in order to start the engine in cold temperatures. The ECM (Engine Control Module) monitors coolant temperature and glow plug voltage, facilitating the plugs heating before and while cranking the engine.

What causes the P0381 code?

This code will be detected if the glow plugs are commanded off, and the voltage feedback is above 2 volts, or if they are commanded on and the feedback is not between 5 and 6.2 volts. Causes of this condition may include:

• Faulty glow plugs
• A faulty glow plug module or timer
• A wiring short in the glow plug heater circuit or harness
• Loose or corroded glow plug circuit connectors
• A faulty glow plug relay
• A blown fuse (which typically has another underlying cause)

What are the symptoms of the P0381 code?

Symptoms of P0381 may include an illuminated Check Engine light, hard start or failure to start, a glow plug indicator lamp which stays on or remains illuminated too long, excessive white exhaust smoke upon startup, excessive noise upon startup, and/or a lit malfunction indicator.

How does a mechanic diagnose the P0381 code?

While the glow plug heater circuit is simpler than many vehicle systems, certain procedures still must be followed to ascertain the source of the problem:

• An OBD-II scanner will be used to obtain stored codes and record freeze frame data.
• The codes will be cleared from the vehicle and retested to see if they reappear.
• The mechanic will perform a visual inspection of the components, including wiring and connectors, to check for corrosion or loose connections.
• An ohmmeter may be used to test individual glow plug connectors to ensure that voltage and ground signals are present.
• Fuses may be tested to see if they blow when the glow plug heater is activated.
• A technician may test the voltage and resistance of the glow plug relay, timer, or module to be sure they match the manufacturer’s specifications.

Common mistakes when diagnosing the P0381 code

Sometimes the timer or relay are replaced without testing the connectors, wiring, and glow plugs. This can result in a continuation of the problem and exaggerated diagnostic and repair costs.

How serious is the P0381 code?

A glow plug heater circuit malfunction can cause the vehicle to start with difficulty, or not to start at all. This could be a dangerous situation when traveling in cold weather because it could leave you stranded in a cold vehicle.

What repairs can fix the P0381 code?

Glow plug heater indicator circuit problems may be fixed by one of the following, depending upon the source of the malfunction:

• Replacement of disconnected, corroded, shorted, or damaged wiring or connectors
• Glow plug relay replacement
• Glow plug timer or module replacement
• Glow plug replacement
• Fuse replacement

Additional comments for consideration regarding the P0381 code

As with any diagnostic trouble code, the stored codes should be recorded and addressed in the order the events occurred. If the codes are cleared from the vehicle and fail to return, this could indicate an intermittent condition, which can be challenging and time-consuming to diagnose. Occasionally an entire fuse bank or PCM may need to be replaced, but these are rare as causes of a P0381 code.

Need help with a P0381 code?

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