U1261

Code

LAND ROVER U — Network/User

SCP (-) circuit failure

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 13 EN: 29 RU: 11

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Page language: EN

Causes

Damaged or chafed SCP (-) wiring harness
Corroded, loose, or bent connector pins at modules or junction connectors
Short to ground or short to battery positive on SCP (-) conductor
Poor chassis or module ground affecting the SCP negative reference
Failed module driving or monitoring the SCP bus
Water ingress, contamination, or bent terminals in connectors

Symptoms

Communication errors or “module not responding” messages on scan tool
Multiple unrelated warning lights (ABS, traction, airbag, engine, etc.)
Loss of specific subsystem functionality (e.g., ABS, BCM, instrument cluster)
Intermittent or permanent fault codes stored in multiple control units
Vehicle may enter limp mode or have degraded performance if critical modules lose communication

What to check

Read all stored and pending codes from all modules; record freeze frame and occurrence history
Identify all modules on the SCP network and note which report loss of communication
Visually inspect SCP wiring harnesses, routing, and connectors for damage, corrosion, or water entry
Check connector mating surfaces and backshells for bent pins or debris
Verify fuses and power/ground supplies to gateway/communication modules
With ignition on, use a multimeter to check continuity of SCP (-) conductor to chassis ground and for unexpected short to battery positive

Signal parameters

SCP (-) conductor should have reliable continuity to vehicle ground; no direct short to battery +
When measured DC to chassis ground, SCP (-) should be near 0 V (as it is the negative/reference conductor) except when measured as part of differential communication signals
Normal wiring continuity: low resistance between connector ends (near 0 ohms); high or infinite resistance indicates open circuit
Waveform: low-voltage communication pulses present on the bus when viewed with a scope — absence or distortion indicates a bus fault

Diagnostic algorithm

Retrieve all U-codes and manufacturer-specific codes from every module; record which modules report SCP-related faults.
Perform a visual inspection of harnesses, grounds, and connectors associated with modules on the SCP bus (gateway, junction boxes, BCM, ECM, ABS/traction modules).
Check main power and ground supplies to the gateway and affected modules; verify fuses and battery connections. Repair any power/ground issues first.
With key ON, measure continuity of the SCP (-) conductor from each end to chassis ground; look for opens, high resistance, or intermittent change during wiggle test.
Measure for shorts: check SCP (-) conductor to battery positive for low resistance (short) and to chassis ground for expected low resistance; isolates any shorted branches by disconnecting connectors and retesting.
Use a scope to check waveform activity and reference level on the SCP bus at different modules; compare to known-good waveform if available.
Isolate the fault location by disconnecting sections of the bus or individual modules one at a time while monitoring for disappearance of the fault code or return of normal signals.
Repair damaged wiring, replace corroded connectors or pins, or replace faulty modules as indicated. Secure and seal connectors to prevent recurrence.
Clear codes and perform a road or operational test to confirm the issue is resolved and codes do not return.
If intermittent and not reproducible, inspect for water intrusion areas and consider replacing suspect connector/junction assemblies; consult technical service bulletins for module or harness updates.

Likely causes

Open or high-resistance SCP (-) conductor due to chafe or broken wire
Corrosion or poor contact at a multi-pin connector (junction box, gateway, or module)
Short to battery (+) or another signal circuit caused by a damaged insulation point
Intermittent connector pin contact caused by vibration or water intrusion
Faulty control module on the SCP network that drags the negative line out of spec

Fault status

⚠️ Status

SCP (-) circuit failure — communication reference/negative conductor open, shorted, or intermittent; network messages disrupted.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 3.0 hours

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