P0381

Code

Generic P — Powertrain

Glow Plug/Heater Indicator Control Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 123 RU: 32

AI status

Completed

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Page language: EN

Causes

Broken or disconnected wiring in the indicator control circuit
Blown fuse or faulty relay for glow plug/heater indicator
Faulty indicator lamp (burned out bulb or LED) or lamp connector
Corroded or poor ground
Damaged connector or pin (terminal loss of continuity)
Faulty ECM/PCM driver output (rare)

Symptoms

Glow-plug/preheat indicator (dash lamp) does not illuminate at key-on preheat
Longer cranking time or harder cold starts (if driver does not activate glow sequence normally)
Possible illumination of MIL or stored fault in engine control module
No visual preheat countdown or incorrect preheat behavior displayed

What to check

Use a scan tool to confirm P0381 is current and review freeze-frame data
Visually inspect wiring, connectors, and ground points for damage or corrosion
Check related fuses and relays for the glow/heater and instrument cluster
Verify the dash indicator lamp works by applying battery voltage at the lamp connector
Measure voltage at the lamp connector during a glow request (key ON preheat) and check for continuity to the ECM
Perform a wiggle test on harness and connectors while monitoring lamp operation and any code responses

Signal parameters

With ignition ON and preheat requested: dash indicator circuit should show a change (battery voltage present or driven to ground depending on design)
Indicator lamp current: typically small (lamp/LED circuit should draw measurable current; if zero, circuit may be open)
Continuity: resistance between indicator lamp and ECM harness should be low (near 0 ohms across short connector runs); open = infinite/very high
Fuse/relay presence: fuse should show battery voltage on both sides; relay contacts should close when energized
No command: ECM output may be high-impedance; when commanded, ECM output will switch (observe voltage change with respect to ground)

Diagnostic algorithm

Verify the code with a scan tool, note freeze-frame and related codes (e.g., other glow-plug or power-relay faults).
Perform a visual inspection of the dash lamp, lamp socket, wiring harness, fuses and relays associated with the glow/heater indicator and preheat system.
Check the indicator lamp operation by applying battery voltage directly to the lamp socket (confirm the lamp itself is not open).
Inspect and test fuses and relays: replace any blown fuses and swap or bench-test relays if required.
With a DVOM, back-probe the indicator circuit at the lamp connector and at the ECM connector. Command the preheat via scan tool (or turn key to preheat) and observe for expected switching (voltage appearing or dropping to ground).
If no voltage change, check continuity between the lamp and ECM. Repair any open wires, corroded connectors, or poor grounds found.
If continuity is good and the lamp is functional, test the ECM output driver for switching. If the ECM does not command the output but other systems are normal, suspect ECM output failure and consult manufacturer procedures before replacement.
After repairs, clear codes and verify proper operation through multiple key cycles and a cold-start check. Re-scan to confirm the code does not return.

Likely causes

Loose or disconnected connector at indicator lamp or ECM
Open fuse or stuck/failed relay in the glow/heater circuit
Broken wire harness (chafing, corrosion, terminal pulled out)
Bad indicator lamp (bulb or LED cluster) or internal lamp circuit open
Failed ECM output transistor for the lamp

Fault status

⚠️ Status

P0381 — Glow Plug/Heater Indicator Control Circuit/Open. ECM detected an open circuit in the glow plug/heater indicator control wiring or components (lamp, fuse, relay, connector, or ECM driver).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours