P0381 The computer found a fault in the glow plug warning lamp circuit on a diesel engine

Glow plug/heater indicator circuit malfunction

Severity not verified — if the car runs badly, have it inspected

The sources define the code and list causes but do not say how serious it is, so severity is not verified.

Source: how we rate severity

P0381 in short

P0381 means the engine computer found a fault in the glow plug indicator lamp circuit on a diesel engine. TroubleCodes.net says the lamp may fail to light or stay on, and lists wiring, a blown bulb, bad grounds, the glow plug relay or fuse and the control module as causes.

On a diesel the warning lamp tells the driver the glow plugs are heating before starting. P0381 is set when the computer sees an electrical fault in that lamp circuit. The Delaware DMV list and TroubleCodes.net give the same meaning.

TroubleCodes.net notes that a lamp that does not light can go with unheated plugs, long cranking or no-start, and a lamp that stays on can go with damaged plugs. It also says all plugs failing at once is extremely rare, so look at the circuit before replacing plugs.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Blown warning bulb, or damaged, corroded or disconnected wiring

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists the warning bulb and wiring and connector damage in the heating circuit.
    What would change this
    Rises if the lamp does not light with the ignition on or wiring is damaged. Falls if the lamp and circuit test good.

  2. Poor ground between battery, engine and body

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists poor grounds.
    What would change this
    Rises if ground cables are loose or corroded or show voltage drop. Falls if grounds test good.

  3. Faulty glow plug relay or blown fuse

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists the relay and fuse.
    What would change this
    Rises if the fuse is blown or the relay does not switch. Falls if both work.

  4. Faulty engine coolant temperature sensor

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists it because the glow system depends on the coolant reading.
    What would change this
    Rises if the sensor reading is wrong. Falls if it matches actual temperature.

  5. Failed glow plug control module or ignition switch

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists the control module and ignition switch.
    What would change this
    Rises if the bulb, wiring, grounds, relay and fuses all test good.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. With the ignition on and the engine off, see whether the glow plug lamp lights, then goes out, as the owner's manual describes.

    Low risk

  2. Check the glow plug fuse, battery and ground cable connections, and look over the connectors for damage or corrosion.

    Low risk

  3. Have a shop test the glow plug relay and control module with a scan tool that can command the circuit.

    Best left to a shopTool: bidirectional scan tool

    Warning:Glow plug circuits draw high current and the engine area stays hot after use. Disconnect the battery and let the engine cool first, and avoid shorting the heavy feed wire.

Symptoms

  • Glow plug lamp does not light, or stays on
  • Long cranking or no start when cold
  • Check engine light is on

How to fix

  1. Turn the ignition on and watch the glow plug lamp, and check the glow plug fuse against the owner's manual.

On your vehicle

Ram

  • 2025–2026 · 2500

    Supported by vehicle data

    Ram bulletin S2609000005 covers a check engine light with P0381-00 and the Wait to Start lamp inoperative on 2025-2026 vehicles. Whether it is still current is not verified.

  • 2025–2026 · 3500

    Supported by vehicle data

    Ram bulletin S2609000005 covers a check engine light with P0381-00 and the Wait to Start lamp inoperative on 2025-2026 vehicles. Whether it is still current is not verified.

  • S2609000005Status unverified

    P0381-00 with the wait-to-start lamp inoperative

    2025–20262500, 3500 · issued · NHTSA 11030430

    Check engine light on with P0381-00 and the Wait to Start lamp inoperative on 2025-2026 Ram heavy duty trucks (2500, 3500, 4500, 5500). Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

  • 2024–2025 · Silverado 2500 HD

    Supported by vehicle data

    Chevrolet bulletin PIP6090 covers DTC P0381 is under investigation and technicians are told to clear the DTC and return the vehicle to the customer on 2024-2025 vehicles. Whether it is still current is not verified.

  • 2024–2025 · Silverado 3500 HD

    Supported by vehicle data

    Chevrolet bulletin PIP6090 covers DTC P0381 is under investigation and technicians are told to clear the DTC and return the vehicle to the customer on 2024-2025 vehicles. Whether it is still current is not verified.

  • PIP6090Status unverified

    DTC P0381 under investigation

    2024–2025silverado-2500-hd, silverado-3500-hd · issued · NHTSA 11024780

    Informs dealer technicians that DTC P0381 is under investigation and to clear the DTC and return the vehicle to the customer, on 2024-2025 Silverado 2500 HD and 3500 HD. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2024–2025 · Sierra 2500 HD

    Supported by vehicle data

    GMC bulletin PIP6090-gmc covers DTC P0381 is under investigation and technicians are told to clear the DTC and return the vehicle to the customer on 2024-2025 vehicles. Whether it is still current is not verified.

  • 2024–2025 · Sierra 3500 HD

    Supported by vehicle data

    GMC bulletin PIP6090-gmc covers DTC P0381 is under investigation and technicians are told to clear the DTC and return the vehicle to the customer on 2024-2025 vehicles. Whether it is still current is not verified.

  • PIP6090-gmcStatus unverified

    DTC P0381 under investigation

    2024–2025sierra-2500-hd, sierra-3500-hd · issued · NHTSA 11024780

    Informs dealer technicians that DTC P0381 is under investigation and to clear the DTC and return the vehicle to the customer, on 2024-2025 Sierra 2500 HD and 3500 HD. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

No curated relationships for P0381 yet.

All Diesel emissions and glow plugs codes

P0381 questions

Does P0381 mean my glow plugs are bad?

Not necessarily. It points to the warning lamp circuit. TroubleCodes.net says it is extremely rare for all the glow plugs to fail at once, so check the lamp, wiring, grounds, relay and fuse first.

Sources and review

  1. TroubleCodes.net P0381: glow plug warning lamp circuit malfunction — TroubleCodes.net
  2. S2609000005: P0381-00 with the wait-to-start lamp inoperative — Ram
  3. PIP6090: DTC P0381 under investigation — Chevrolet
  4. PIP6090-gmc: DTC P0381 under investigation — GMC
  5. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
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