U2521

Code

LAND ROVER U — Network/User

CAN bus — invalid data received from module

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 29 EN: 47 RU: 31

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Page language: EN

Causes

Corroded, loose or damaged CAN wiring or connectors
Short to battery or ground on CANH or CANL
Missing or incorrect bus termination (open or wrong resistance)
Faulty or failing control module transmitting malformed frames
Multiple ECUs with mismatched baud rate or message configuration
Low battery/unstable supply voltage affecting module operation

Symptoms

MIL or multiple warning lamps illuminated
Loss or limited functionality of systems that share the CAN bus (e.g., instrument cluster, ABS, HVAC, gateway functions)
Intermittent or permanent diagnostic communication failures with affected module
Unusual or flickering instrument cluster messages or data
Other communication-related DTCs present

What to check

Read all U- and manufacturer-specific codes from all modules; note which modules report communication errors
Inspect relevant wiring harnesses and connectors for corrosion, bent pins, chafing or water damage
Measure CAN bus termination resistance (typical ~60 Ω across CANH-CANL with ignition off; verify vehicle spec)
Check battery voltage and charging system stability
Confirm correct CAN bus baud rate and bus architecture for the vehicle model/year
Use a scope or CAN analyzer to capture frames, check for malformed frames, bus errors, or dominant/continuous states

Signal parameters

Idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (verify with vehicle-specific spec)
Dominant state: CANH ~3.5 V and CANL ~1.5 V (approximate values; check with scope)
Termination: two 120 Ω resistors in parallel (approx. 60 Ω total) across CANH–CANL (verify spec)
Typical bus speeds: 250 kbps or 500 kbps (confirm vehicle network rate)
Look for continuous dominant (stuck low) or continuous recessive (open) conditions on the bus

Diagnostic algorithm

Retrieve and document all stored codes and freeze-frame data from all modules; note time of occurrence and any correlated events.
Clear codes and attempt to reproduce; observe whether U2521 returns and under what conditions (startup, driving, after accessory use).
Visually inspect connectors and wiring for the modules implicated by the code and the vehicle's CAN topology (gateway/junction boxes). Repair any obvious damage.
Measure termination resistance across CANH–CANL with ignition off; expected value ~60 Ω (consult vehicle spec). Repair/replace termination if out of spec.
Use a scan tool to monitor live CAN traffic and compare expected CAN IDs and message frequency. Note missing or malformed frames.
Use an oscilloscope or CAN bus analyzer to view physical layer signals for noise, voltage offsets, stuck dominant/recessive states, or corrupted frames.
Isolate segments: disconnect non-critical modules or harness branches (one at a time) to identify whether a particular module causes invalid frames.
Verify module power and ground integrity for any module suspected of sending invalid data; check reference voltages and battery stability.
If a module is identified as the source, check for available software updates/reprogramming; reflash or reprogram per manufacturer procedure before replacement.
Replace the module only after confirming it is the root cause; after repair, clear codes and confirm no recurrence and proper operation of affected systems.

Likely causes

Poor connector/cable connection at the module or gateway
A single module transmitting invalid frames (faulty module)
Improper termination or a short on the CAN network
Module software version mismatch after recent replacement or update

Fault status

⚠️ Status

U2521 — CAN bus: invalid data received from module

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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