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Home / DTC / B2378 — Body Control Module Supply Voltage Low

B2378 — Body Control Module Supply Voltage Low

Detailed page for trouble code B2378.

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22,491specific
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Code

B2378

LAND ROVER B — Body

Body Control Module Supply Voltage Low

Brand: LAND ROVER
Type: B — Body
AI status
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Completed 100%
Page language: EN

Causes

  • Weak or discharged battery
  • Poor battery terminals or cable connections (corrosion, loose)
  • Faulty or slipping alternator/charging system
  • Blown fuse or fusible link in BCM supply circuit
  • Damaged wiring or connector to BCM (short, high resistance, open)
  • Poor or corroded ground(s) for BCM

Symptoms

  • Multiple body electrical failures (lights, locks, windows, HVAC controls)
  • Warning lights or messages on instrument cluster
  • Intermittent or total loss of remote locking or alarm
  • Communication errors with other modules (CAN/UH communication faults)
  • Engine may crank but electronics behave erratically
  • Codes stored for other modules or lost-communication DTCs

What to check

  • Use a scan tool to read stored and pending DTCs and capture freeze frame data
  • Measure battery voltage at rest, with ignition ON, and with engine running
  • Inspect battery terminals, cables and chassis/engine grounds for tightness and corrosion
  • Check fuses and fusible links related to the BCM power feed
  • Visually inspect wiring and BCM connector for damage, corrosion or water ingress
  • Backprobe BCM power pin(s) and ground pin(s) while observing voltage with key ON and during cranking

Signal parameters

  • Battery rest voltage: normally ~12.4–12.8 V (vehicle off)
  • Ignition ON (accessory/run) expected at battery voltage; normal operating/charging voltage with engine running ~13.5–14.8 V
  • During cranking voltage may drop temporarily (commonly to ~9–11 V); long, deep drops indicate battery/charging issue
  • BCM supply pin should show stable voltage comparable to battery/charging voltage with ignition ON
  • Ground circuit resistance should be low (near 0 Ω); high resistance can cause local voltage drop

Diagnostic algorithm

  1. Record full scan tool report (all modules) and note any related U or B codes and freeze frame data.
  2. Visually inspect battery, terminals, main cables and all primary grounds. Clean and tighten as required.
  3. Measure and record battery voltage at the battery posts. If below ~12.2 V, charge or test battery and retest.
  4. Start engine and measure charging voltage at battery. Verify alternator is producing ~13.5–14.8 V.
  5. Inspect and test fuses/fusible links that feed the BCM; replace any blown devices and retest.
  6. Backprobe BCM power and ground pins. With ignition ON and engine running, verify stable supply voltage and good ground. Note any voltage drops under load/cranking.
  7. If supply or ground is low or intermittent, trace wiring to source (battery/alternator/fuse) and repair damaged wiring, connectors or grounds.
  8. If wiring, fuses and charging are good but fault persists, perform wiggle tests on harness/connector while monitoring voltages to find intermittent connector pins or internal faults.
  9. After repairs, clear codes and perform a functional test and a short road test to confirm no recurrence. If BCM still reports low supply and wiring is confirmed good, consider module fault and follow manufacturer procedures for BCM replacement and programming.
  10. Always follow vehicle-specific safety, immobilizer and service procedures when removing or replacing the BCM; disconnect battery when performing harness repairs as required.

Likely causes

  • Battery state of charge or poor battery connections
  • Charging system not maintaining proper voltage
  • Loose/corroded ground or power feed at BCM connector
  • Blown fuse/fusible link feeding BCM
  • Wiring harness damage between battery/alt and BCM

Fault status

⚠️ Status
Body Control Module supply voltage below minimum threshold detected by BCM.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

U0100 U0121 U0140 B1000 B1234
283

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