P0382 Glow plug heater circuit B malfunction OBD-II

P0382 Glow plug heater circuit B malfunction (OBD-II)

Overview

• What it is: P0382 indicates a fault in the glow plug heater circuit for bank B (cylinder bank B) where the PCM detects a abnormal condition in the circuit-specifically a high input/activation signal in that circuit. In many vehicles, glow plugs are used to aid starting (diesel or some cold-start systems in engines with glow devices). The fault is classified as a powertrain (P0xxx) OBD-II code.
• How this code fits in the system: P0xxx codes are powertrain codes (part of the OBD-II standard). This code is generated by the vehicle's PCM/control module when the glow plug circuit B is not behaving within expected electrical parameters. Source context: OBD-II documentation places P0 codes in the powertrain category.

What This Code Means

• Definition .
• Additional context: OBD-II DTCs are stored/flagged when the diagnostic monitors detect parameters outside expected ranges; P0xxx are powertrain-related, and glow-plug related faults fall under this umbrella. This provides the framework for diagnosing P0382 within the PCM's monitoring.
• Practical takeaway: P0382 is a circuit-level fault in the B-side glow plug/heater wiring; it often points to a short, open, or control issue in the B circuit, or a fault within the PCM driver for that circuit.

Symptoms

• Delayed or hard starting, especially in cold conditions (glow plugs assist cold-start; a fault can prolong crank time).
• MIL (Check Engine Light) illumination with P0382 stored or pending.
• Inconsistent starting performance or occasional misfire symptoms during startup as the glow-heater function fails to operate reliably.
• Engine may run roughly after initial startup if the glow plug circuit fault affects warm-up behavior (more common on diesels; on some engines with glow systems, cold-start aids may be reduced).

Important nuance about causes and vehicle type

• Glow plug systems are common on diesel engines; some gasoline engines use glow-related starting aids in certain regions or designs. The P0382 code is tied to the B-side glow-plug circuit, so the exact physical layout (how many plugs, which bank is B) will vary by engine. General diagnostic steps apply across platforms, but component accessibility and wiring diagrams will differ by model.

Probable Causes

• Most common cause: Faulty glow plug(s) or a compromised B-bank glow plug harness/connector (short to power, corrosion, damaged insulation). Likely contributor to a high input reading or failed circuit operation. Probability: 40-60%
• Wiring harness faults in the B circuit (short to battery or open/loose connection, damaged insulation, contact resistance). Probability: 20-30%
• PCM/driver circuit fault (driver transistor or control logic stuck high, or PCM input conditioning issue). Probability: 5-15%
• Blown fuse or failed relay (if your system uses a dedicated relay/fuse for the glow plug circuit). Probability: 5-10%
• Component-level short to ground in the B circuit or an intermittent fault (less common, but possible). Probability: 2-5%

Diagnostic Approach

1) Confirm and document the DTC

• Use an OBD-II scan tool to confirm P0382 is active or stored, and note any related codes (e.g., P0380, P0383, or other misfire/engine start codes).
• Record freeze-frame data (engine coolant temp, RPM, ambient temp, run time since key-on, battery voltage) to establish starting conditions.

2) Review service information and wiring diagrams

• Obtain the vehicle's wiring diagram for the glow plug system and identify the B bank circuit path, connector locations, and any known service bulletins for glow plug wiring in your model.
• Confirm whether the system uses a glow plug relay, a PCM driver, or direct PCM switching for circuit B (logic varies by design).

3) Inspect the B-circuit wiring and connectors

• Visually inspect the harness and connectors for the B bank glow plugs: signs of heat damage, corrosion, melted insulation, or loose/dirty connections.
• Check for damaged or pinched wires in the B circuit path (from PCM/driver to the glow plugs).
• Verify fuse status (and relay operation if applicable). Replace any blown fuses or failed relays as required.

4) Check the battery and charging condition

• Measure battery voltage with engine off and engine running; low voltage can cause incorrect PCM readings and affect glow-plug control.
• Ensure the charging system can supply sufficient current for heated circuits during startup.

5) Inspect and test the B-bank glow plug(s)

• If accessible, perform a resistance check on each glow plug in bank B using a suitable ohmmeter. Compare readings to manufacturer specifications.
• Look for open circuits (infinite resistance) or markedly high resistance indicating a bad glow plug element.
• If the plant design uses a single high-resistance glow plug or an individual plug per cylinder, test each plug to locate a failed unit.

6) Test the B-circuit integrity and PCM drive

• With the ignition key on (engine off) or during a cold-start cycle as appropriate for your platform, use a multimeter to verify that the B circuit voltage is present at the glow plug harness connector when commanded by the PCM.
• If voltage is present in the circuit at all times (or not present when commanded), investigate the wiring and PCM driver. A stuck-high reading may indicate a short or a PCM driver fault.
• If voltage is not present when commanded, re-check the fuse/relay and wiring back to the PCM.

7) Check for related faults and monitors

• Review other DTCs that may indicate related engine-start or harness faults (e.g., misfire, battery/charging system issues, or other glow-plug circuit codes).
• Some vehicles provide a glow-plug test or self-test via the scan tool; perform any available circuit test to verify operation.

8) Consider PCM/ECU implications

• If all wiring and glow plugs test within spec and no wiring fault is found, the issue could be a PCM/driver fault. In this case, assess software/firmware versions, and consider PCM replacement or re-flash if supported by the manufacturer.
• Before replacing the PCM, confirm no intermittent electrical fault is present and that the symptom is reproducible.

9) Repair and verification

• Replace failed glow plug(s) in bank B and repair or replace damaged wiring/connectors in the B circuit as needed.
• Replace failed fuse/relay if identified as the root cause.
• Reassemble, clear codes, and perform a road test to verify that P0382 does not reoccur.
• Re-scan after test drive to verify that the code does not return and to confirm all related readiness monitors pass.

Testing and measurement tips

• Use a wiring diagram to identify the exact B-circuit path and node voltages.
• When measuring glow-plug resistance, ensure the engine is cool and the glow plugs are isolated to avoid measurement errors due to surrounding circuitry.
• If performing a live data test, observe the PCM's demand for glow-plug activation and compare it with actual circuit voltage at the glow plug harness during a cold start.

Safety Considerations

• Glow plug circuits (especially in diesel engines) can carry significant current during start; ensure engine off before disconnecting plugs and use proper PPE.
• When testing high-current or high-voltage portions of the system, be mindful of stored energy and risk of shock; follow vehicle-specific safety procedures.
• Disconnect the battery or follow proper procedure when working with the PCM or critical wiring to avoid accidental data loss or ECU faults.

Documentation

• Document all findings, measurements, and components replaced.
• After repairs, re-scan for P-codes, observe live data for proper glow-plug operation during cold-start, and confirm that the vehicle no longer triggers P0382.
• Check for any related codes that may appear after initial repair to confirm the issue is fully resolved and that no secondary faults were introduced.

Key source references used for this guide

• Wikipedia: OBD-II
  • Diagnostic Trouble Codes overview (definition of how DTCs are generated and organized within OBD-II; P0xxx as powertrain codes). This provides the broader framework for interpreting P0382 as a powertrain code.
• GitHub (open-source code definitions)
  • Code definition: (Glow plug heater circuit B malfunction). This provides the direct association of P0382 with the glow plug heater circuit B.
• Contextual guidance from OBD-II materials
  • The general operation of OBD-II DTCs and their role in monitoring engine and emissions-related parameters is covered in the OBD-II sections of the OBD-II article. This informs the diagnostic approach, including the use of freeze-frame data, readiness monitors, and the role of the PCM in generating DTCs.

Notes

• do not include NHTSA complaint data for P0382, so probability estimates above rely on professional experience and typical circuit-fault patterns rather than published complaint statistics.
• The exact diagnosis and repair steps can vary by engine family and year, particularly depending on whether the system uses a glow plug relay, a direct PCM drive, or separate control logic. Always cross-check with the vehicle's service information and wiring diagrams for model-specific procedures.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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