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Home / DTC / P0384 — Glow Plug Control Module 1 Control Circuit High

P0384 — Glow Plug Control Module 1 Control Circuit High

Detailed page for trouble code P0384.

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22,491specific
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Code

P0384

Generic P — Powertrain

Glow Plug Control Module 1 Control Circuit High

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring harness to Glow Plug Control Module 1
  • Corroded, loose or damaged connector at the control module or glow plug bank
  • Failed glow plug control module (internal driver transistor or electronics)
  • Stuck or welded glow plug relay / contact
  • Bad or high-resistance ground to the control module or glow plug bank
  • One or more shorted / high-resistance glow plugs causing abnormal circuit behavior

Symptoms

  • Malfunction indicator lamp (MIL) or glow plug warning lamp illuminated
  • Hard cold starting or extended cranking time
  • Diesel engine running rough at start-up or increased white/gray smoke on start
  • Poor preheat performance (dashboard glow light behavior abnormal)
  • Possible diagnostic trouble codes related to glow/heater circuits

What to check

  • Read and record freeze-frame and all related DTCs with a scan tool
  • Visually inspect connectors, wiring harness and glow plug module for damage or corrosion
  • Check battery voltage (should be ~12.6 V at rest, ~13.5–14.8 V when running)
  • Inspect fuses and relays in the glow plug/heater circuit
  • Check module and engine grounds for secure connection and continuity
  • Check glow plug resistances (one-by-one) at cold to see for obvious shorts/open circuits

Signal parameters

  • Expected control line voltage when module OFF: approx. battery voltage (11–15 V)
  • Expected control line voltage when module ON (driver active): near 0–1 V if module pulls line to ground, or switched to ground/current sink depending on design
  • PWM control frequency (varies by manufacturer): commonly from 1 Hz up to tens of Hz; some systems use higher frequencies—refer to OEM data
  • Typical glow plug resistance (varies by engine): commonly 0.2–2.0 ohms each; check OEM specs
  • Typical current per glow plug: from a few amps up to 20 A depending on plug and system; total module current depends on number of plugs

Diagnostic algorithm

  1. Connect a capable scan tool, read and save freeze-frame data and all related codes (P0384 plus any P03xx).
  2. Clear codes and attempt to re-create the fault to confirm persistence. Note conditions (cold start, key-on, engine-run).
  3. Perform a careful visual inspection of the glow plug control module, wiring harness, connectors and relays for corrosion, bent pins, melted insulation or rodent damage.
  4. With battery charged, check battery voltage at the battery and at module power pin with key ON and engine running to confirm supply.
  5. Check continuity and resistance of the ground(s) for the module and glow-plug bank. Clean and secure grounds as needed.
  6. Backprobe/control-pin measurements: with scan tool commanding preheat ON, measure control circuit voltage. Compare to expected behavior: it should change from battery voltage to near 0 V (or PWM as specified). If the control line stays high when commanded ON, suspect open/short to power or failed module driver.
  7. Measure individual glow plug resistances (engine cold). Compare to spec and look for shorted (very low) or open/high-resistance plugs. Replace any plugs out of spec.
  8. Inspect and test glow plug relay(s) if used: verify coil and contact operation. Replace if contacts are welded or coil is defective.
  9. If wiring, relay and plugs are good, test the control module: verify inputs from ECM and outputs to plugs. If available, swap with a known-good module or bench-test module per OEM procedure.
  10. If module replacement is required, replace module, clear codes, perform any required relearn procedures and re-test under the same conditions to verify repair.
  11. If fault persists after module replacement, inspect ECM outputs and communication; consult OEM wiring diagrams and consider ECM testing/replacement.

Likely causes

  • Damaged wiring or poor connector (corrosion, bent pins) between ECM and glow plug control module
  • Failed glow plug control module (driver electronics)
  • Poor ground connection at module or glow-plug bank
  • Stuck relay/contact or a shorted glow plug

Fault status

⚠️ Status
Glow Plug Control Module 1 control circuit voltage is higher than expected when the ECM commanded the glow/heater circuit. The ECM flagged the circuit as 'Control Circuit High'. This can prevent proper preheating and cause hard starts.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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Code

P0384

LAND ROVER P — Powertrain

Control of the control module of incandescent bulb - high circuit

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring harness to Glow Plug Control Module 1
  • Corroded, loose or damaged connector at the control module or glow plug bank
  • Failed glow plug control module (internal driver transistor or electronics)
  • Stuck or welded glow plug relay / contact
  • Bad or high-resistance ground to the control module or glow plug bank
  • One or more shorted / high-resistance glow plugs causing abnormal circuit behavior

Symptoms

  • Malfunction indicator lamp (MIL) or glow plug warning lamp illuminated
  • Hard cold starting or extended cranking time
  • Diesel engine running rough at start-up or increased white/gray smoke on start
  • Poor preheat performance (dashboard glow light behavior abnormal)
  • Possible diagnostic trouble codes related to glow/heater circuits

What to check

  • Read and record freeze-frame and all related DTCs with a scan tool
  • Visually inspect connectors, wiring harness and glow plug module for damage or corrosion
  • Check battery voltage (should be ~12.6 V at rest, ~13.5–14.8 V when running)
  • Inspect fuses and relays in the glow plug/heater circuit
  • Check module and engine grounds for secure connection and continuity
  • Check glow plug resistances (one-by-one) at cold to see for obvious shorts/open circuits

Signal parameters

  • Expected control line voltage when module OFF: approx. battery voltage (11–15 V)
  • Expected control line voltage when module ON (driver active): near 0–1 V if module pulls line to ground, or switched to ground/current sink depending on design
  • PWM control frequency (varies by manufacturer): commonly from 1 Hz up to tens of Hz; some systems use higher frequencies—refer to OEM data
  • Typical glow plug resistance (varies by engine): commonly 0.2–2.0 ohms each; check OEM specs
  • Typical current per glow plug: from a few amps up to 20 A depending on plug and system; total module current depends on number of plugs

Diagnostic algorithm

  1. Connect a capable scan tool, read and save freeze-frame data and all related codes (P0384 plus any P03xx).
  2. Clear codes and attempt to re-create the fault to confirm persistence. Note conditions (cold start, key-on, engine-run).
  3. Perform a careful visual inspection of the glow plug control module, wiring harness, connectors and relays for corrosion, bent pins, melted insulation or rodent damage.
  4. With battery charged, check battery voltage at the battery and at module power pin with key ON and engine running to confirm supply.
  5. Check continuity and resistance of the ground(s) for the module and glow-plug bank. Clean and secure grounds as needed.
  6. Backprobe/control-pin measurements: with scan tool commanding preheat ON, measure control circuit voltage. Compare to expected behavior: it should change from battery voltage to near 0 V (or PWM as specified). If the control line stays high when commanded ON, suspect open/short to power or failed module driver.
  7. Measure individual glow plug resistances (engine cold). Compare to spec and look for shorted (very low) or open/high-resistance plugs. Replace any plugs out of spec.
  8. Inspect and test glow plug relay(s) if used: verify coil and contact operation. Replace if contacts are welded or coil is defective.
  9. If wiring, relay and plugs are good, test the control module: verify inputs from ECM and outputs to plugs. If available, swap with a known-good module or bench-test module per OEM procedure.
  10. If module replacement is required, replace module, clear codes, perform any required relearn procedures and re-test under the same conditions to verify repair.
  11. If fault persists after module replacement, inspect ECM outputs and communication; consult OEM wiring diagrams and consider ECM testing/replacement.

Likely causes

  • Damaged wiring or poor connector (corrosion, bent pins) between ECM and glow plug control module
  • Failed glow plug control module (driver electronics)
  • Poor ground connection at module or glow-plug bank
  • Stuck relay/contact or a shorted glow plug

Fault status

⚠️ Status
Glow Plug Control Module 1 control circuit voltage is higher than expected when the ECM commanded the glow/heater circuit. The ECM flagged the circuit as 'Control Circuit High'. This can prevent proper preheating and cause hard starts.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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P0380 P0385 P0386 P0387 P0388 P0389
320

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