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Home / DTC / C1991 — Module failure in calibration

C1991 — Module failure in calibration

Detailed page for trouble code C1991.

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22,461specific
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Code

C1991

LAND ROVER C — Chassis

Module failure in calibration

Brand: LAND ROVER
Type: C — Chassis
Views: UK: 18 EN: 30 RU: 15
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Page language: EN

Causes

  • Interrupted or failed software flash/update
  • Corrupt calibration data or incorrect calibration loaded
  • Incompatible or incorrect module software/part number
  • Loss of power or unstable battery voltage during programming
  • Internal module hardware failure
  • Faulty wiring, poor ground, or connector corrosion causing data errors

Symptoms

  • Malfunction indicator lamp or specific system warning on dash
  • System or feature associated with the module is disabled or inoperative
  • Error message on instrument cluster (e.g., ‘service [system]’)
  • Vehicle may enter limp-home or reduced functionality mode for affected system
  • Multiple related communication or calibration DTCs stored

What to check

  • Read all stored DTCs (current, pending, historic) and note freeze-frame/occurrence data
  • Check battery condition and charging system voltage (recommended >12.6 V before programming)
  • Visual inspection of module connectors and wiring for corrosion, damage, or water ingress
  • Verify module part number, software (SW) and calibration (cal) versions against OEM data
  • Check CAN/LIN network status and for other network-related DTCs (U-codes)
  • Confirm VIN and vehicle option data match module calibration

Signal parameters

  • Module supply voltage (VBatt) — should be stable and within specified range (typically >12V)
  • Module ground integrity (low resistance to chassis ground)
  • CAN bus status: active, error counters, bus load and voltage levels
  • Module software version and calibration ID (compare to OEM history)
  • Module programming/flash status flags or event logs
  • Communication response time and message frequency for module messages

Diagnostic algorithm

  1. Capture all DTCs and freeze-frame data. Save a report for reference before clearing codes.
  2. Verify battery state-of-charge and charging system. Charge or connect stable power supply if below recommended threshold.
  3. Inspect connectors and wiring to the module. Repair any corrosion, damaged pins, or loose connections.
  4. Check for related network DTCs (U-codes). Diagnose and repair CAN/LIN bus faults first if present.
  5. Confirm the module part number, SW and calibration IDs using OEM diagnostic tool. Note mismatches with vehicle VIN/options.
  6. Attempt a re-read of calibration data and, if supported, re-initiate calibration or reflash procedure using manufacturer-approved diagnostic equipment.
  7. If reflash fails, record error messages from the programming tool. Retry after ensuring stable battery and using manufacturer guidance (correct tool version, cable, and server access).
  8. If multiple reflash attempts fail or calibration continues to report corrupted data, swap with a known-good module (if available) or request module bench repair/replacement following OEM procedures.
  9. After successful calibration/reflash, clear codes and perform relearn procedures as required by the OEM. Test-drive and monitor for return of C1991 or related codes.
  10. If fault persists after correct software and known-good hardware, escalate to manufacturer technical support and check for updated calibration/ECU hardware bulletins.

Likely causes

  • Failed or incomplete reflash/update (most common)
  • Battery voltage dropped during programming
  • Module contains wrong calibration for vehicle VIN or option set
  • Intermittent CAN bus or connector fault corrupting calibration data
  • Module internal memory/processor fault

Fault status

⚠️ Status
Module calibration failure detected. The control module reports corrupted or incorrect calibration data or an unsuccessful calibration process. Reprogramming/re-calibration or module service is required to restore correct operation.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.0-3.5 hours

Similar codes

C1990 C1992 U0100 U1900 P0606
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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