Range Rover CAN Bus Faults: Multiple Warnings, One Root Cause

A Range Rover arrives with suspension warnings, traction control faults, parking brake errors, and an inoperative infotainment system — all at once. The instinct is to assume catastrophic failure across multiple systems. In reality, a single CAN bus fault is usually responsible for every symptom. The network is the problem, not the individual modules.

Short Answer

The Controller Area Network (CAN bus) in a Range Rover connects 60 to 80+ electronic control units on multiple network segments. When one segment develops a fault — a short circuit, open circuit, or termination resistor failure — every module on that segment loses communication. Each module then independently logs fault codes for every other module it can no longer talk to. The result is dozens of fault codes and multiple dashboard warnings from a single wiring fault. Diagnosing by fault code alone leads to replacing modules that are perfectly functional. The correct approach is to diagnose the network itself: measure bus resistance, check signal integrity with an oscilloscope, and isolate the faulty segment before touching any parts.

What You'll Learn

• How the CAN bus network is structured in Range Rover models (L405, L322, L460)
• Why a single fault creates cascading warnings across unrelated systems
• The difference between high-speed CAN, medium-speed CAN, and LIN sub-buses
• How to distinguish a network fault from a genuine module failure
• Why oscilloscope diagnosis is essential for CAN bus fault tracing
• Common physical causes of CAN bus faults in JLR vehicles

Real-World Scenarios

Case 1: L405 Range Rover — 23 Fault Codes, One Corroded Connector

A 2016 L405 Range Rover arrived with air suspension fault, HDC unavailable, parking brake warning, traction control warning, and no instrument cluster communication. A previous garage had quoted for a new air suspension module, a new ABS module, and a new instrument cluster — over £4,500 in parts alone. We performed a full network topology scan using JLR Pathfinder and identified that the MS-CAN (medium-speed CAN) bus had abnormal resistance — 38 ohms instead of the expected 60 ohms. Physical inspection traced the fault to a corroded splice connector behind the left-hand B-pillar trim, where water ingress from a blocked sunroof drain had been wicking along the harness. We repaired the connector, cleared all 23 stored fault codes, and every system returned to full function. Total parts cost: £0. The fault was entirely in the wiring.

Case 2: L322 Range Rover — Intermittent Total Electrical Shutdown

A 2009 L322 Range Rover experienced random complete electrical shutdowns while driving — instruments would blank, the engine would continue running, then everything would return seconds later. This vehicle had been to three workshops. One replaced the instrument cluster. Another replaced the CJB (Central Junction Box). Neither fixed it. The root cause was a fractured CAN bus wire inside the driver's door harness flex section — the rubber boot between the A-pillar and door. Every time the door was opened to a certain angle, the wire broke contact. An oscilloscope captured the dropout in real-time by monitoring the CAN-H and CAN-L signals while manipulating the door. A harness repair resolved the fault permanently.

Case 3: 2020 Range Rover Sport — Phantom Gearbox Fault

A Range Rover Sport P400 displayed "Gearbox Fault — Reduced Performance" intermittently. The transmission itself was functioning correctly. Fault code analysis revealed a CAN communication timeout between the TCM (Transmission Control Module) and the ECM (Engine Control Module). Both modules were healthy. The issue was a failing CAN bus termination resistor inside the ECM connector. When the engine bay reached operating temperature, the resistor value drifted, causing intermittent signal reflections on the HS-CAN bus. Replacing the connector housing and resistor pack eliminated the fault. The gearbox never had a problem.

Why Inspection and Diagnostics Matter

CAN bus faults are the single most misdiagnosed category of failure on modern JLR vehicles. The reason is straightforward: most garages diagnose by reading fault codes and replacing the module that the code points to. On a CAN bus fault, every code is a symptom, not a cause. Replacing modules based on fault codes alone is expensive and ineffective.

At Nine Torque, CAN bus diagnosis follows a structured process. We start with a full system scan to establish the scope of the fault — how many modules are affected and which network segment they share. We then measure the CAN bus resistance at the diagnostic port (expected values: 60 ohms for a dual-terminated bus, 120 ohms for a single termination). If the resistance is abnormal, we systematically isolate segments by pulling fuses to individual modules until the faulty segment is identified. We then use a dual-channel oscilloscope to verify signal integrity — checking for correct voltage levels (CAN-H at 3.5V, CAN-L at 1.5V during dominant state), clean transitions, and absence of signal reflections.

This approach takes longer than plugging in a code reader, but it finds the actual fault instead of generating a parts bill. If your Range Rover is displaying multiple unrelated warnings, contact us before authorising any module replacements. The root cause is almost certainly cheaper than you've been quoted.

Frequently Asked Questions

How do I know if my Range Rover has a CAN bus fault rather than multiple individual faults?

The key indicator is simultaneous onset. If four or five warnings appeared at the same time — or within the same ignition cycle — it is almost certainly a network issue. Genuine independent failures across multiple systems at the same moment are statistically improbable. If the warnings appeared gradually over weeks, individual faults become more likely.

Can a flat battery cause CAN bus fault codes?

Yes. A battery voltage below approximately 10.5V causes modules to brown out and lose CAN communication. This stores "lost communication" codes across the network. If your Range Rover was jump-started or had a flat battery, a full fault code clear after charging is the first step. If the codes return, there is a genuine fault. If they stay clear, the low battery was the sole cause. See our post on Range Rover battery drain for related information.

Are certain Range Rover models more prone to CAN bus faults?

The L322 (2002-2012) is the most susceptible due to its age and the use of splice connectors in the harness that corrode over time. The L405 (2013-2021) is more robust but suffers from water ingress issues, particularly around the sunroof drain paths and rear boot area. The new L460 uses Ethernet-based communication for many systems, which changes the fault profile but does not eliminate network issues.

Can I drive with CAN bus warnings showing?

It depends on which systems are affected. If the CAN fault has disabled the ABS, traction control, or air suspension, driving is not recommended — these are safety-critical systems. If the fault is confined to comfort or infotainment functions, the vehicle is generally safe to drive to a specialist. However, CAN bus faults can be intermittent and may worsen, so prompt diagnosis is advisable.

Why can't my garage find the fault with their diagnostic tool?

Most generic diagnostic tools read fault codes but cannot perform network topology analysis. They will show you the symptom codes (e.g., "lost communication with module X") but cannot measure bus resistance, capture CAN signal waveforms, or isolate network segments. Manufacturer-level diagnostics combined with oscilloscope testing is required for accurate CAN bus fault tracing.