What this code means
B1664 may mean the body control module is detecting an open condition in the rear interior low-frequency antenna line for the keyless access system.
What the vehicle may do
- The vehicle may store the code during a keyless access system self check.
- Keyless access behavior may be inconsistent around the rear interior antenna area.
- Some vehicles may have no obvious driver complaint beyond the stored code.
Possible fault areas
- Possible open wiring or poor connection in the rear interior LF antenna circuit.
- Possible rear interior LF antenna issue.
- Possible body control module-side issue.
Diagnostic path
Open with what B1664 means
On this 2020 to 2025 Honda CR-V Hybrid, B1664 points to the rear interior LF antenna circuit being seen as open by the keyless access system. In plain terms, the body control module may not be seeing the antenna circuit it expects. The vehicle may have inconsistent keyless access behavior around the rear interior area, or it may simply store the code during a self check. The likely fault areas are broad at first: the rear interior LF antenna circuit, the antenna itself, connector issues, or a possible body control module-side problem.
Start with the basic checks
Before troubleshooting, take a minute to review the general troubleshooting approach for this system. Then start with the basic system checks and follow a structured diagnostic approach. If other codes are present, check what they mean first instead of treating B1664 in isolation. After that, run the HDS Self Check. That gives you the system status before you start disconnecting connectors and measuring the antenna circuit.
Check the antenna circuit for an open
The first hands-on check is the open-wire inspection for the EXT_M plus and EXT_M minus circuits. For preparation, disconnect the rear interior LF antenna 2-pin connector and body control module connector C, the 66-pin connector. With those female terminals disconnected and IG Mode OFF, perform the open-wire inspection. A normal result for the EXT_M plus circuit is less than 1 Ω, and a normal result for the EXT_M minus circuit is also less than 1 Ω. If either side is abnormal, the diagnostic path points to a problem in the circuit.
Check the body control module side
If the external circuit checks normal, move to the body control module inspection. For this check, the external circuit has to be normal first. Disconnect the rear interior LF antenna 2-pin connector. With the rear interior LF antenna connector male terminals disconnected and IG Mode ON, inspect the module internal circuit. The expected result is voltage. If that inspection is abnormal, the diagnostic path points to a problem with the body control module.
Use the remaining result to isolate the antenna
If the circuit inspection is normal and the body control module inspection is normal, the remaining fault area is the rear interior LF antenna. At that point, the path has narrowed B1664 down to a problem with the rear interior LF antenna rather than the wiring run or the body control module side.
Close
This diagnostic path can be run as an overall check before other inspections, because it covers the key inspection areas for this code. But if a broad check fails, do not guess. Continue isolating the failed inspection item so you know whether the problem is in the circuit, the body control module side, or the rear interior LF antenna. The takeaway: B1664 is an open-circuit style diagnosis, so prove the wiring first, prove the module-side output next, and only then call the antenna as the remaining fault area. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1664 is best approached by separating the diagnosis into circuit continuity, body control module-side inspection, and then the rear interior LF antenna as the remaining fault area.
For more guided automotive diagnostics, visit STEP Diagnostics.
