What this code means
B1664 may mean the body control module is seeing a possible open or disconnected condition in the rear interior LF antenna circuit for the keyless access system.
What the vehicle may do
- Keyless access operation may be intermittent.
- Fob detection inside the cabin can be inconsistent.
- The concern may be most noticeable when the system is trying to confirm key location inside the vehicle.
Possible fault areas
- Possible rear interior LF antenna issue.
- Possible wiring or connector issue in the rear interior LF antenna circuit.
- Possible body control module side issue after the external circuit checks normal.
Diagnostic path
Code meaning and first checks
B1664 is a keyless access code for the rear interior LF antenna circuit. In plain language, the body control module may be seeing that rear interior antenna line as open or disconnected. The vehicle may have intermittent keyless access behavior or inconsistent fob detection inside the cabin. The broad fault areas are the rear interior LF antenna, the antenna wiring and connectors, and, only after the outside circuit checks normal, the body control module side of the circuit. Before you chase the code, start with the basic keyless access system checks. If other codes are present, check what they mean first and follow the proper network diagnostic path before treating this code by itself. Then run the HDS Self Check so you know what the system is reporting right now.
Open-wire check on the antenna circuit
Next, move to the open-wire inspection for the rear interior LF antenna circuit. Disconnect the rear interior LF antenna connector, which is a 2P connector. Also disconnect body control module connector C, which is a 66P connector. With those disconnected, perform the EXT_R+ and EXT_R- open-wire checks at the specified connector points. Both sides are judged normal only when the inspection shows less than 1 Ω. If either side is abnormal, the fault is in the circuit, so stay with the wiring and connection path instead of jumping ahead to the module or antenna.
Body control module side of the circuit
Once the external circuit is normal, the body control module inspection becomes valid. The precondition matters here: the outside circuit has to be normal first. For this check, disconnect the rear interior LF antenna 2P connector and perform the module internal circuit inspection. The normal result is voltage. The module has a permanent power supply, so this check applies whether the vehicle mode is ON or OFF, LOCK. If this inspection is abnormal, the problem is with the body control module side of the system. If it fails, keep the diagnosis tied to the failed inspection item and avoid guessing.
Rear interior LF antenna decision
If the circuit inspection is normal and the body control module inspection is normal, then the remaining item in this diagnostic path is the rear interior LF antenna. At that point, the rear interior LF antenna is the indicated cause. The important part is the order: confirm the wiring path first, confirm the module side only after the external circuit is normal, and leave the antenna as the conclusion only when the other inspections check out.
Takeaway
For B1664, do not shortcut the diagnosis. This is a circuit-open style path: scan it, check the antenna circuit for continuity, prove the body control module side only under the right precondition, and then make the rear interior LF antenna decision last. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1664 often needs a circuit-first diagnosis before making a decision on the antenna or the body control module.
For more guided automotive diagnostics, visit STEP Diagnostics.
