What does it mean?
B1605 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Keyless Access Control Unit Lost Communication With MICU (MICU Message) .
Symptoms
- Security indicator stays lit continuously, including with the key removed
- The indicator no longer flashes to show the armed state, so alarm status cannot be read
- Lighting or cluster fuse blows
- Small constant current draw flattens the battery over several days
- On the keyless variant, the smart key is not recognised, touch lock and unlock fail and push-button start does not respond
Likely causes
- Indicator wire chafed against a powered circuit behind the dash, holding the lamp on
- Wrong bulb or an aftermarket LED wired to a constant supply instead of the module output
- Module output driver damaged and pulling the circuit high
- Connector terminal displaced and bridging to a powered pin
- Damage during a previous cluster, radio or accessory installation
- Corroded splice where moisture has bridged the indicator wire to a live circuit
- On applications where this code refers to keyless access, that unit losing its expected message from the body control unit through bus wiring, power, ground or module failure
How to fix it
- With the key off, measure the indicator circuit at the module and look for battery voltage where the output should be off
- Disconnect the cluster and repeat the measurement to separate the cluster from the harness
- Inspect the loom behind the dash for insulation worn through onto a powered wire
- Remove any aftermarket lighting or accessory taps in the cluster area and retest
- Check the connector for a terminal pushed out of place onto a live pin
- Repair the harness before replacing the module, since a fresh module will simply fail again on a shorted circuit
- On the keyless variant, check the unit power, ground and bus connection and look for water intrusion at its mounting position