P1612 – Immobilizer Communication Error (Toyota)

Description

The ECM detected a communication failure between the immobilizer system and the engine control module.

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Symptoms

No start condition
Security light on
Key not recognized
Intermittent start
Failsafe mode

Causes

Faulty immobilizer ECU
Wiring issues
Connector corrosion
Weak battery voltage
ECM communication fault

Diagnosis

Check wiring
Inspect connectors
Measure battery voltage
Test immobilizer ECU
Scan for related codes

Repair

Repair wiring
Clean connectors
Replace immobilizer ECU
Replace ECM if needed