B1C38

Code

LAND ROVER B — Body

Master unlock switch trava

Brand: LAND ROVER

Type: B — Body

Views: UK: 20 EN: 24 RU: 31

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Page language: EN

Causes

Broken or damaged wiring in master unlock switch circuit
Corroded, loose or contaminated connector at the switch or BCM
Internal failure of the master unlock switch
Short to ground or to battery voltage in the harness
Water ingress or contamination in the door switch area
Faulty BCM or module software/firmware error (less common)

Symptoms

Driver master lock/unlock switch does not unlock doors or is intermittent
Other door locks may not respond to master switch
Central locking may only work with the remote keyfob or not at all
DTC present and may reappear after clearing
Possible fuse or relay issues if short is severe

What to check

Read freeze frame and fault status with a diagnostic scanner; check for related body/locking DTCs
Attempt to operate master unlock switch while watching live data for switch input state
Visual inspection of driver door harness, switch connector and BCM connector for corrosion, damaged wires, or water ingress
Check fuses and locking relays for damage
Wiggle test the harness and switch while monitoring live data to reproduce intermittent faults
Measure voltage and continuity between switch connector and BCM

Signal parameters

Rest state: switch circuit typically open or held at battery voltage via pull-up (vehicle-specific). Expect stable voltage when not actuated (e.g., ~0–12 V depending on design)
Actuation: closed circuit to ground or to +12 V depending on implementation — signal should change state reliably when pressed
Resistance: switch contact resistance should be low when closed (near 0 ohms) and high when open (OL)
No PWM or chatter on the line when switch is steady; intermittent toggling indicates poor connection or failing switch

Diagnostic algorithm

Connect a diagnostic scan tool and read B1C38 fault details, test results, and any associated DTCs. Record freeze-frame data.
Clear the code, then operate the master unlock switch repeatedly while monitoring the live input parameter to confirm if the code returns and to reproduce the failure.
Visually inspect switch, connector, and harness in driver door for damage, corrosion, or water. Open the switch connector and inspect pins for corrosion, bent pins or contamination.
With ignition on, backprobe the switch connector and measure voltage at rest and while operating the switch. Compare to expected behavior (signal should change cleanly when actuated).
Perform continuity check between the switch connector pins and the BCM input pin with connectors unplugged; inspect for short to ground or battery, and for high resistance indicating broken conductor.
Wiggle the harness and connectors while observing the live signal; intermittent changes indicate wiring or connector issue.
If wiring and connector check good, remove the switch and bench-test or substitute with a known-good switch to confirm operation.
If replacement switch cures the problem, re-test and clear codes. If fault persists and wiring is good, consider BCM input circuit test or module diagnosis and consult manufacturer service information for module repair/reprogramming.
After repair, clear DTCs and perform several lock/unlock cycles to confirm fault does not return.

Likely causes

Failed master unlock switch (dirty contacts or internal failure)
Connector pin corrosion or bent pins at the switch or BCM
Wiring chafing causing intermittent short or open
Water entry into door causing intermittent signal or corrosion

Fault status

⚠️ Status

Master unlock switch circuit fault detected (B1C38). The driver master unlock input is reporting an electrical fault (open/short/intermittent). Central locking may not respond to the master switch.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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