B1C37

Code

LAND ROVER B — Body

Master

Brand: LAND ROVER

Type: B — Body

Views: UK: 13 EN: 27 RU: 22

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Page language: EN

Causes

Faulty or failed master switch/module (internal electronics fault)
Damaged, corroded or loose connector at the master unit
Open, shorted or high-resistance wiring between master and body control module (BCM)
Poor ground or battery supply to the master unit
Blown fuse or fuse link supplying the master circuit
Intermittent CAN/LIN communication fault between master unit and control modules

Symptoms

Partial or complete loss of function of the master control (e.g., windows, mirrors, central locks) associated with the master unit
Intermittent operation of controlled systems (functions work sometimes)
Warning or message displayed in the instrument cluster related to the affected system
DTC stored in vehicle diagnostic memory and may reappear after clearing
Unresponsive switches or delayed response when operated

What to check

Read and record all stored DTCs and freeze-frame/confirmation data with an OEM-capable scan tool
Visual inspection of the master switch/module, connector, and wiring for corrosion, bent pins, water ingress or physical damage
Check relevant fuses and fusible links for continuity and correct rating
Measure battery voltage at the master unit connector with key on to confirm adequate supply (nominal 12–14 V)
Verify good ground(s) at the master unit and related modules
Check for communication (CAN/LIN) presence using a scan tool or oscilloscope

Signal parameters

Supply voltage at master connector: ~12.0–14.5 V (key on/engine running as applicable)
Ground: near 0 V with low resistance to chassis ground
Switch output signals: logic-level voltages per OEM spec (often 0 V or battery voltage), verify change when operated
Communication bus activity: CAN high/low differential signals present (~2.5 V idle; +/- ~1 V swing) or LIN single-wire frames
Continuity/resistance of wiring to BCM: near 0 Ω for power/ground, low-ohms per OEM spec for supply/ground
No short to battery or short to ground on any switch circuits

Diagnostic algorithm

Connect an OEM-capable scan tool; read and record all DTCs, freeze frame and related module data. Note confirmation count and fault status.
Inspect the master switch/module area for signs of water ingress, corrosion, physical damage or intrusion of foreign material.
Verify related fuses and relays; replace any blown fuses and re-check the fault after clearing codes.
With the ignition on, measure supply voltage at the master unit power pin(s) and check ground continuity to chassis ground.
Operate the master switch while monitoring live data and relevant signal lines with the scan tool or oscilloscope to confirm signal changes or loss.
Inspect and backprobe the connector pins for bent or pushed-out terminals; wiggle harness while observing live data to detect intermittent faults.
Check communication bus (CAN/LIN) for presence and errors; compare to other modules that remain online.
If wiring and power/ground are good, remove the master switch/module and bench-test per OEM procedure (or substitute a known-good unit if available).
If the module fails bench tests or substitution cures the fault, replace the master unit. If communication errors persist, trace and repair bus wiring or address affected module(s).
After repair, clear codes, cycle ignition, and perform full functional test to confirm repair. Re-scan to ensure code does not return and document the repair.

Likely causes

Corroded/loose connector at the master switch
Failed master switch/module electronics
Low battery voltage or blown fuse to the master circuit
Intermittent communication fault on vehicle network (CAN/LIN)

Fault status

⚠️ Status

B1C37 — Master control/module circuit fault (electrical or communication fault detected in the master control assembly).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours

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