P1621

Code

Other P — Powertrain

Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match

Brand: Other

Type: P — Powertrain

Views: UK: 36 EN: 70 RU: 41

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Page language: EN

Corrupted or failed module internal memory (EEPROM/flash)
Battery low/voltage loss causing lost non-volatile memory
Replacement or reprogramming of one control module without updating immobilizer code words
Key/transponder data not learned or mismatched
CAN/serial communication errors between immobilizer and engine control module
Damaged wiring, connectors, or ground to immobilizer or PCM/BET module

Use a capable scan tool to read freeze frame, full DTC list and any manufacturer-specific immobilizer codes
Check battery voltage and charging system (battery >=12.4 V at rest; >=13.5–14.5 V when running)
Inspect fuses and power/ground circuits for the affected control module(s)
Visually inspect connectors and wiring at PCM/BCM/immobilizer and antenna/transponder ring for damage or corrosion
Confirm whether any module was recently replaced or reflashed
Test key/transponder recognition with dealer or advanced scanner (verify spare key)

Read and record all DTCs and freeze frame data with a full-feature scan tool; note related codes (communication, power, immobilizer).
Check battery state and charging system; ensure stable power during diagnostics and programming. Replace or charge battery if low.
Visually inspect and secure all fuses, power and ground connections to the PCM/BCM/immobilizer and antenna ring; repair corrosion/damage.
Verify whether any control module has been recently replaced or reflashed; obtain module part numbers and software levels. If modules were swapped, confirm correct programming and VIN/immobilizer pairing.
Use the factory or advanced scanner to read immobilizer memory status, number of learned keys, and any manufacturer-specific data (EEPROM/flash health).
Attempt the manufacturer-prescribed immobilizer/key re-learn or synchronization procedure (follow factory tool prompts). Test with original and spare keys.
If communication errors are present, diagnose CAN/serial wiring and termination, check continuity and resistance between modules, and repair wiring faults.
If memory corruption or module internal failure is suspected (EEPROM/flash fault), consider module reflash/update or replacement and then perform full immobilizer reprogramming. Only replace/control program modules per manufacturer procedures.
After repairs or reprogramming, clear DTCs and perform road/test or start cycles to confirm code does not return. If code returns, escalate to module bench test or OEM support.