What this code means
B1646 may mean the keyless access control unit is seeing the driver door low frequency antenna circuit as open.
What the vehicle may do
- Keyless access at the driver door may be unreliable.
- One-push start or keyless functions can be affected depending on how the system is using the driver door antenna.
Possible fault areas
- Possible driver door outer handle antenna concern.
- Possible loose or poor connector contact.
- Possible open or high resistance in the antenna wiring.
- Possible keyless access control unit concern.
Diagnostic path
Opening context
B1646 on this Accord is for the driver door LF antenna circuit being seen as open by the keyless access control unit. In plain terms, the system may not be seeing the driver door outside antenna the way it expects to. The driver may notice keyless access behavior at the driver door can be unreliable, and the possible fault areas are the door handle antenna, the connector and wiring between the handle and the control unit, or the keyless access control unit itself. Work this one in order, because the first check tells you whether the code is current or just an intermittent connection issue.
Confirm whether B1646 is current
Start by verifying the problem with the HDS. Clear the DTCs, go into the MODE MENU, enter SELF CHECK, run the SELF CHECK, and then check for DTCs again. If B1646 comes right back, move into the circuit checks. If B1646 is not indicated, treat it as an intermittent failure. The system is OK at that moment, so look closely for loose or poor connections before going any deeper.
Check the control unit output to the driver door antenna
With B1646 confirmed, check the EXT FR DR+ and EXT FR DR- line output from the keyless access control unit. Press the engine start/stop button to select the OFF mode, then disconnect the driver's door outer handle 8P connector. Press the engine start/stop button again to select the ON mode. On the HDS, select KEYLESS ACCESS CONTROL from the ONE-PUSH START system select menu, enter FUNCTIONAL TESTS, and connect the voltmeter across the driver door outer handle connector. Test point 1 is the driver's door outer handle 8P connector No. 2, GRN. Test point 2 is the driver's door outer handle 8P connector No. 6, BLU. Then select DRIVER'S DOOR ANTENNA with the HDS. The decision here is simple: is there voltage or not? If there is voltage, the driver's door LF antenna is faulty, and the repair path is to replace the driver's door outer handle. If there is no voltage, keep going and check the two wires for an open.
Check the EXT FR DR wiring for an open
For the open-wire check, press the engine start/stop button to select the OFF mode. Disconnect keyless access control unit connector A, the 32P connector. At this point, the keyless access control unit connector A 32P and the driver's door outer handle 8P connector are both disconnected. Check continuity on each line. For EXT FR DR+, check between keyless access control unit connector A 32P No. 29, GRN, and the driver's door outer handle 8P connector No. 2, GRN. For EXT FR DR-, check between keyless access control unit connector A 32P No. 13, BLU, and the driver's door outer handle 8P connector No. 6, BLU. If both paths have continuity, the diagnostic path points to replacing the keyless access control unit. If continuity is missing, repair the open or high resistance in the wire.
Takeaway
The takeaway is to confirm B1646 first, then separate the fault by checking output at the driver door handle and continuity back to the keyless access control unit. That keeps you from guessing between the handle antenna, the wiring, and the control unit. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often narrowed down by confirming whether it is current, checking for antenna output at the door handle connector, and then checking continuity in the antenna circuits.
For more guided automotive diagnostics, visit STEP Diagnostics.
