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Home / DTC / U0421 — Invalid Data Received From Suspension Control Module A

U0421 — Invalid Data Received From Suspension Control Module A

Detailed page for trouble code U0421.

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U0421

Generic U — Network/User

Invalid Data Received From Suspension Control Module A

Brand: Generic
Type: U — Network/User
Views: UK: 19 EN: 63 RU: 21
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Corroded, loose, or damaged wiring/connectors to the suspension control module
  • Faulty suspension control module (SCM A) or internal memory/data corruption
  • CAN/LIN bus communication errors or missing termination
  • Low or unstable vehicle battery/charging system voltage during communication
  • Software mismatch or outdated/incorrect programming in SCM A or other network modules
  • Intermittent connector contact due to moisture, vibration, or pin damage

Symptoms

  • Suspension warning or malfunction lamp illuminated
  • Related stability/ABS traction faults or warning lights may appear
  • Incorrect ride height, uneven ride, or loss of adaptive damping control
  • Intermittent or permanent loss of suspension features (e.g., auto-leveling, adaptive modes)
  • Stored U-codes or other communication errors when scanned with a diagnostic tool
  • Possible degraded vehicle handling or reduced safety-system coordination

What to check

  • Connect a capable scan tool and record freeze frame, permanent codes, and full DTC list from all modules
  • Check vehicle battery voltage and charging system at rest and while waking modules (should be stable and within manufacturer spec)
  • Visually inspect SCM A connector, pins, and wiring for corrosion, bent pins, or water intrusion
  • Inspect nearby harness for chafing, heat damage, or repairs that could affect CAN/LIN wires
  • Scan for other U-codes or CAN bus-related DTCs to identify network-wide issues
  • Check for Technical Service Bulletins (TSBs) or software updates for SCM A and related modules

Signal parameters

  • Expected message ID(s) from SCM A (varies by make/model) — verify reception on CAN/LIN bus with scan tool or scope
  • Message frequency: suspension state messages typically 5–50 Hz depending on signal (verify against OEM spec)
  • Data length code (DLC) commonly 8 bytes for CAN messages; check for truncated/altered length
  • Presence and validity of checksum or CRC fields where used by the module protocol
  • Bus idle and dominant waveform presence on CAN high/low when ECU is awake (verify using scope or CAN tester)

Diagnostic algorithm

  1. Retrieve and record all DTCs and freeze frame data from all modules. Note whether multiple modules report invalid data from SCM A.
  2. Verify battery voltage and charging system health. Recharge or stabilize battery if low and retest communications.
  3. Visually inspect SCM A connector and harness for damage, corrosion, or moisture. Repair or clean terminals as needed.
  4. With ignition on, use a scan tool to attempt communication with SCM A. Note error messages, response timeouts, or partial data.
  5. Check for other network DTCs (U-codes) that indicate bus-wide issues. If multiple modules fail to see SCM A, suspect network/termination or power/ground.
  6. Perform a wiggle test on harness while monitoring live data and CAN traffic; look for intermittent changes or dropouts.
  7. Measure CAN bus physical layer with an oscilloscope or dedicated CAN tester: verify differential signal, voltage levels, and termination resistance per manufacturer spec.
  8. If physical layer and wiring are good, attempt reprogram/reflash of SCM A software using OEM procedures; ensure correct calibration for vehicle option package.
  9. Clear codes and perform a road test or exercise suspension functions while monitoring live data to confirm resolution.
  10. If module remains nonfunctional after wiring and software verification, follow OEM replacement procedure for SCM A and reprogram/configure as required.

Likely causes

  • Open, short, or high-resistance circuit in SCM A power, ground, or communication lines
  • Faulty SCM A hardware (processor, memory, I/O) after ruling out wiring and power
  • CAN bus termination resistor missing or shorted, causing message corruption
  • Corroded connector pins or water intrusion at SCM A connector
  • Module software incompatibility after a service/part replacement or failed reflash

Fault status

⚠️ Status
Invalid data received from Suspension Control Module A — communication or data integrity issue on vehicle network with the suspension control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0415 U0416 U0100 U0121 U0140
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Code

U0421

HYUNDAI U — Network/User

Invalid Data Received From Ride Level Control Module

Brand: HYUNDAI
Type: U — Network/User
Views: UK: 17 EN: 32 RU: 15
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Corroded, loose, or damaged wiring/connectors to the suspension control module
  • Faulty suspension control module (SCM A) or internal memory/data corruption
  • CAN/LIN bus communication errors or missing termination
  • Low or unstable vehicle battery/charging system voltage during communication
  • Software mismatch or outdated/incorrect programming in SCM A or other network modules
  • Intermittent connector contact due to moisture, vibration, or pin damage

Symptoms

  • Suspension warning or malfunction lamp illuminated
  • Related stability/ABS traction faults or warning lights may appear
  • Incorrect ride height, uneven ride, or loss of adaptive damping control
  • Intermittent or permanent loss of suspension features (e.g., auto-leveling, adaptive modes)
  • Stored U-codes or other communication errors when scanned with a diagnostic tool
  • Possible degraded vehicle handling or reduced safety-system coordination

What to check

  • Connect a capable scan tool and record freeze frame, permanent codes, and full DTC list from all modules
  • Check vehicle battery voltage and charging system at rest and while waking modules (should be stable and within manufacturer spec)
  • Visually inspect SCM A connector, pins, and wiring for corrosion, bent pins, or water intrusion
  • Inspect nearby harness for chafing, heat damage, or repairs that could affect CAN/LIN wires
  • Scan for other U-codes or CAN bus-related DTCs to identify network-wide issues
  • Check for Technical Service Bulletins (TSBs) or software updates for SCM A and related modules

Signal parameters

  • Expected message ID(s) from SCM A (varies by make/model) — verify reception on CAN/LIN bus with scan tool or scope
  • Message frequency: suspension state messages typically 5–50 Hz depending on signal (verify against OEM spec)
  • Data length code (DLC) commonly 8 bytes for CAN messages; check for truncated/altered length
  • Presence and validity of checksum or CRC fields where used by the module protocol
  • Bus idle and dominant waveform presence on CAN high/low when ECU is awake (verify using scope or CAN tester)

Diagnostic algorithm

  1. Retrieve and record all DTCs and freeze frame data from all modules. Note whether multiple modules report invalid data from SCM A.
  2. Verify battery voltage and charging system health. Recharge or stabilize battery if low and retest communications.
  3. Visually inspect SCM A connector and harness for damage, corrosion, or moisture. Repair or clean terminals as needed.
  4. With ignition on, use a scan tool to attempt communication with SCM A. Note error messages, response timeouts, or partial data.
  5. Check for other network DTCs (U-codes) that indicate bus-wide issues. If multiple modules fail to see SCM A, suspect network/termination or power/ground.
  6. Perform a wiggle test on harness while monitoring live data and CAN traffic; look for intermittent changes or dropouts.
  7. Measure CAN bus physical layer with an oscilloscope or dedicated CAN tester: verify differential signal, voltage levels, and termination resistance per manufacturer spec.
  8. If physical layer and wiring are good, attempt reprogram/reflash of SCM A software using OEM procedures; ensure correct calibration for vehicle option package.
  9. Clear codes and perform a road test or exercise suspension functions while monitoring live data to confirm resolution.
  10. If module remains nonfunctional after wiring and software verification, follow OEM replacement procedure for SCM A and reprogram/configure as required.

Likely causes

  • Open, short, or high-resistance circuit in SCM A power, ground, or communication lines
  • Faulty SCM A hardware (processor, memory, I/O) after ruling out wiring and power
  • CAN bus termination resistor missing or shorted, causing message corruption
  • Corroded connector pins or water intrusion at SCM A connector
  • Module software incompatibility after a service/part replacement or failed reflash

Fault status

⚠️ Status
Invalid data received from Suspension Control Module A — communication or data integrity issue on vehicle network with the suspension control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0415 U0416 U0100 U0121 U0140
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

U0421

LAND ROVER U — Network/User

Invalid data received from the level control module March

Brand: LAND ROVER
Type: U — Network/User
Views: UK: 10 EN: 21 RU: 10
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Corroded, loose, or damaged wiring/connectors to the suspension control module
  • Faulty suspension control module (SCM A) or internal memory/data corruption
  • CAN/LIN bus communication errors or missing termination
  • Low or unstable vehicle battery/charging system voltage during communication
  • Software mismatch or outdated/incorrect programming in SCM A or other network modules
  • Intermittent connector contact due to moisture, vibration, or pin damage

Symptoms

  • Suspension warning or malfunction lamp illuminated
  • Related stability/ABS traction faults or warning lights may appear
  • Incorrect ride height, uneven ride, or loss of adaptive damping control
  • Intermittent or permanent loss of suspension features (e.g., auto-leveling, adaptive modes)
  • Stored U-codes or other communication errors when scanned with a diagnostic tool
  • Possible degraded vehicle handling or reduced safety-system coordination

What to check

  • Connect a capable scan tool and record freeze frame, permanent codes, and full DTC list from all modules
  • Check vehicle battery voltage and charging system at rest and while waking modules (should be stable and within manufacturer spec)
  • Visually inspect SCM A connector, pins, and wiring for corrosion, bent pins, or water intrusion
  • Inspect nearby harness for chafing, heat damage, or repairs that could affect CAN/LIN wires
  • Scan for other U-codes or CAN bus-related DTCs to identify network-wide issues
  • Check for Technical Service Bulletins (TSBs) or software updates for SCM A and related modules

Signal parameters

  • Expected message ID(s) from SCM A (varies by make/model) — verify reception on CAN/LIN bus with scan tool or scope
  • Message frequency: suspension state messages typically 5–50 Hz depending on signal (verify against OEM spec)
  • Data length code (DLC) commonly 8 bytes for CAN messages; check for truncated/altered length
  • Presence and validity of checksum or CRC fields where used by the module protocol
  • Bus idle and dominant waveform presence on CAN high/low when ECU is awake (verify using scope or CAN tester)

Diagnostic algorithm

  1. Retrieve and record all DTCs and freeze frame data from all modules. Note whether multiple modules report invalid data from SCM A.
  2. Verify battery voltage and charging system health. Recharge or stabilize battery if low and retest communications.
  3. Visually inspect SCM A connector and harness for damage, corrosion, or moisture. Repair or clean terminals as needed.
  4. With ignition on, use a scan tool to attempt communication with SCM A. Note error messages, response timeouts, or partial data.
  5. Check for other network DTCs (U-codes) that indicate bus-wide issues. If multiple modules fail to see SCM A, suspect network/termination or power/ground.
  6. Perform a wiggle test on harness while monitoring live data and CAN traffic; look for intermittent changes or dropouts.
  7. Measure CAN bus physical layer with an oscilloscope or dedicated CAN tester: verify differential signal, voltage levels, and termination resistance per manufacturer spec.
  8. If physical layer and wiring are good, attempt reprogram/reflash of SCM A software using OEM procedures; ensure correct calibration for vehicle option package.
  9. Clear codes and perform a road test or exercise suspension functions while monitoring live data to confirm resolution.
  10. If module remains nonfunctional after wiring and software verification, follow OEM replacement procedure for SCM A and reprogram/configure as required.

Likely causes

  • Open, short, or high-resistance circuit in SCM A power, ground, or communication lines
  • Faulty SCM A hardware (processor, memory, I/O) after ruling out wiring and power
  • CAN bus termination resistor missing or shorted, causing message corruption
  • Corroded connector pins or water intrusion at SCM A connector
  • Module software incompatibility after a service/part replacement or failed reflash

Fault status

⚠️ Status
Invalid data received from Suspension Control Module A — communication or data integrity issue on vehicle network with the suspension control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0415 U0416 U0100 U0121 U0140
Workshop Manuals

Repair manuals for LAND ROVER

3

Land Rover Defender 300Tdi — Workshop Manual (1996 model year)

Workshop Manual
Defender 300Tdi Years: 1996 Manual in English 7.5 MB
Short description

Official workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.

199,00 UAH
Contents
Key sections:
  • 01 INTRODUCTION
  • 04 GENERAL SPECIFICATION DATA
  • 05 ENGINE TUNING DATA
  • 07 GENERAL FITTING REMINDERS
  • 09 LUBRICANTS, FLUIDS AND CAPACITIES
  • 10 MAINTENANCE
  • 12 ENGINE Tdi
  • - Description and operation
  • - Fault diagnosis
  • - Adjustment
  • - Repair and overhaul procedures
  • 19 FUEL SYSTEM Tdi
Buy

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Workshop Manual
Defender Years: 1999–2002 Manual in English 7.6 MB
Short description

Workshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.

199,00 UAH
Contents
Key sections:
  • 01 - INTRODUCTION
  • - Introduction
  • - Dimensions
  • - References
  • - Repairs and replacements
  • - Poisonous substances
  • - Fuel handling precautions
  • - Synthetic rubber
  • - Recommended sealants
  • - Used engine oil precautions
  • - Accessories and conversions
  • - Wheels and tyres
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Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)

Workshop Manual
Manual in English Pages: 494 7.1 MB
Short description

Land Rover Range Rover Electrical Library (LRL 0453ENG). Comprehensive manual covering fuse details, earth points, system descriptions, diagnostics and connector pin-outs for electrical troubleshooting and repair. Intended for technicians and service workshops.

199,00 UAH
Contents
Key sections:
  • 1 INTRODUCTION
  • 1.1 About this document
  • 1.2 Battery voltage
  • 1.3 Electrical precautions
  • 1.4 Battery disconnecting / charging
  • 1.5 Disciplines / greases
  • 1.6 Abbreviations
  • 1.7 HeVAC, sensors abbreviations
  • 1.8 How to use this document
  • 1.9 Connector detail format
  • 1.10 Fault diagnosis
  • 1.11 Wire colour codes
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