P0383

Code

LAND ROVER P — Powertrain

Control of the control module of incandescent bulb - low circuit

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 22 EN: 64 RU: 25

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Page language: EN

Causes

Blown fuse supplying glow plug/heater control module
Faulty glow plug control module or relay
Open, corroded or shorted wiring/connectors between ECM and control module
Poor ground(s) at the control module or engine wiring harness
Low battery voltage or weak battery
Water intrusion or corrosion in connector or module

Symptoms

Extended cranking or hard starting, especially in cold conditions
Glow plug / pre-heat warning lamp illuminated or flashing
Malfunction Indicator Lamp (MIL) may be stored
Rough idle after cold start or increased smoke on start
Loss of glow plug/heater function or reduced heater performance

What to check

Read and record all stored DTCs and freeze‑frame data; note conditions (battery voltage, temperature)
Verify battery state of charge and charging system voltage (should be ~12–14 V with ignition on/engine running)
Visually inspect fuses, relays and related fusebox terminals for damage or blown fuse
Inspect connectors and wiring for corrosion, bent pins, damaged insulation, or water ingress
Check for proper ground connections at engine and control module
Measure voltage at the glow plug/heater control module connector with key ON and during a pre‑heat cycle

Signal parameters

Control module supply voltage: approx. battery voltage (≈ 11–14 V) with ignition ON
Control/command signal from ECM: normally toggles between ~0 V and battery voltage (pulse width varies during pre‑heat)
Resistance of individual glow plugs/heaters: generally low (fractions of an ohm to a few ohms); expect low overall circuit resistance
Ground continuity: near 0 Ω between module ground and chassis ground
If voltage at module is significantly below battery or signal is absent/intermittent, fault is likely in wiring, fuse, relay, or module

Diagnostic algorithm

Confirm the code and capture freeze‑frame. Note battery voltage and engine temp when code set.
Verify battery condition and charging system. Recharge or replace weak battery before further testing.
Inspect fuses and relays related to glow plug/heater circuit; replace any blown fuse and retest.
Visually inspect connectors and wiring to the glow plug control module and ECM for corrosion, damage, or loose pins; repair as required.
With connector connected, measure supply voltage and ground at the control module with ignition ON and during pre‑heat; compare to battery voltage.
Check continuity and resistance of control wiring between ECM and the control module; look for opens, high resistance, or shorts to ground/battery.
If wiring and supply are good, bench‑test or substitute the glow plug control module or relay (if a known‑good unit available) and recheck operation.
If control module replacement does not clear the issue, check ECM outputs and consider ECM diagnostic or software update per technical service information.
After repairs, clear codes and perform a few key cycles and cold start test to confirm code does not return.

Likely causes

Corroded or loose connector at the glow plug/heater control module
Failed glow plug control relay or module
Damaged wiring harness (open or short to ground) in heater control circuit
Blown fuse for glow plug/heater circuit
Low battery voltage during key-on or crank

Fault status

⚠️ Status

ECU detected low voltage/low signal on the glow plug/heater control module circuit. Pre‑heat/heater control may be impaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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P0383 — Control of the control module of incandescent bulb - low circuit