P18A8

Code

LAND ROVER P — Powertrain

Rear differential lock motor - Brake control

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 15 EN: 33 RU: 23

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Page language: EN

Causes

Open, short or high resistance in wiring between rear differential lock motor and brake/control module
Poor or corroded connector or ground at the motor or control module
Failed rear differential lock motor/actuator
Brake control module or differential lock module internal fault or software error
Blown fuse or faulty relay supplying the lock motor
Mechanical binding or seized differential lock preventing normal motor operation

Symptoms

Rear differential lock will not engage or disengage on command
Warning lamp/message for differential lock or driveline/brake system on the dash
Fault stored in vehicle ECU(s) related to differential lock or brake control
Inability to use specific drive modes that require diff lock (4x4 functions)
Possible related ABS/traction control warnings or degraded traction control operation

What to check

Read and record all related fault codes and freeze frame data from drivetrain and brake/ABS modules
Check battery voltage and charging system; ensure nominal 12–14.5 V during tests
Inspect harness and connectors at the rear diff lock motor and brake control module for damage, corrosion or water ingress
Check fuses and relays for the differential lock motor circuit
Scan for CAN/communication errors between brake/ABS module and diff-lock controller
Attempt commanded actuation while monitoring live data and observe motor/feedback response

Signal parameters

Supply voltage to lock motor: approx. vehicle battery voltage (12–14.5 V) when commanded
Control signal: PWM or switched supply from brake/lock module (varies by model—observe live data)
Motor coil resistance: consult vehicle-specific service data; typical low-ohm value (check for open/short)
Motor current draw during operation: elevated during stall or binding, normal spec during free rotation
CAN bus messages: diff-lock status and brake module communications (check for lost messages or errors)

Diagnostic algorithm

Retrieve and record all related DTCs from engine, ABS/brake and transfer/differential modules. Note freeze frame and occurrence conditions.
Clear codes and attempt to reproduce the fault by commanding rear diff lock while monitoring battery voltage and live data.
Visually inspect the wiring harness, connectors and grounds at the rear diff lock motor and control modules. Repair any damage or corrosion.
Verify fuses/relays for the motor circuit. Replace any blown fuses or faulty relays and re-test.
With connector disconnected, measure resistance across the actuator terminals and compare to factory spec (checks for open/short).
Command the actuator while measuring supply voltage at the motor connector. If supply present but motor doesn’t run, bench-test motor by applying controlled 12 V and observe operation.
If motor draws excessive current or is seized, remove and inspect actuator and mechanical locking mechanism for binding or damage.
Check for and repair any CAN or module communication faults. Reflash or update module software if bulletins recommend.
After repairs, clear codes and perform required calibration/learn procedures for the differential lock system per service manual.
Road test and re-check for stored codes to confirm fault is resolved.

Likely causes

Damaged wiring harness to the rear diff lock motor (chafing, rodent damage, broken conductor)
Corroded/loose connector at motor, ground or module
Motor windings open or shorted (actuator failure)
Brake control/vehicle dynamics module inhibiting actuator due to a sensor fault
Battery/vehicle voltage too low during actuation or intermittent supply

Fault status

⚠️ Status

Rear differential lock motor - Brake control fault detected

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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P18A8 — Rear differential lock motor - Brake control