What this code means
B1648 may indicate a possible open in the passenger door low-frequency antenna circuit for the keyless access system.
What the vehicle may do
- The keyless access system may behave inconsistently near the passenger door.
- The vehicle may store the code during a keyless access self check.
- Some vehicles can show little obvious driver-facing behavior beyond the stored fault.
Possible fault areas
- Possible passenger door low-frequency antenna or outside handle area issue.
- Possible wiring, terminal fit, connector, open, or high-resistance condition in the antenna circuit.
- Possible keyless access control unit involvement.
Diagnostic path
Open and context
On this Accord, B1648 points to a possible open in the passenger door low-frequency antenna circuit used by the keyless access system. The customer may notice keyless entry or one-push start behavior that is inconsistent around the passenger door area, or the system may simply store the code during its self check. Broadly, this can involve the passenger door antenna built into the outside handle area, the antenna wiring and connectors, or the keyless access control unit. The key here is not to guess at the handle or the module. The test sequence separates a control-unit output problem from an open or high-resistance circuit.
Confirm the code first
Start by clearing the DTCs with the HDS. From the mode menu, enter the self check, run the self check, and then check for DTCs again. If B1648 comes right back, continue into the circuit test. If B1648 does not return, treat it as an intermittent at this time. The system is considered OK right now, so concentrate on loose terminals, poor connector fit, or connection issues in the affected passenger door antenna circuit.
Check the antenna drive output
With B1648 confirmed, press the engine start/stop button to select OFF mode, then disconnect the front passenger's door outer handle 8P connector. Turn the vehicle back to ON mode. In the HDS, select Keyless Access Control from the one-push start system menu, go into functional tests, and set up a voltmeter between the two antenna circuit pins at the disconnected handle connector: No. 2, green, and No. 6, blue. Then command the front passenger door antenna functional test. At this point, you are checking whether the keyless access control unit is actually driving that antenna circuit. If voltage is present, the diagnostic path calls the front passenger's door LF antenna faulty, and the repair is to replace the front passenger's door outer handle. If there is no voltage, keep going to the open-wire check before condemning anything.
Check the two antenna wires for an open
For the open-wire check, turn the system back to OFF mode. Disconnect keyless access control unit connector A, 32P, while keeping the front passenger's door outer handle 8P connector disconnected. Now check continuity on each side of the antenna circuit. For EXT FR AS plus, check between keyless access control unit connector A, No. 22, green, and the handle connector No. 2, green. For EXT FR AS minus, check between keyless access control unit connector A, No. 6, blue, and the handle connector No. 6, blue. 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.
Wrap-up and verification mindset
The clean way through B1648 is: confirm the code, check whether the control unit can drive the passenger door antenna circuit, then check the two antenna wires before making the call. Use the HDS self check and DTC check as the confirmation point so you know B1648 is no longer indicated. For more diagnostic training, visit stepdiagnostics.com.
Final check
Confirm the code, test the antenna drive output, then prove the two circuit paths before deciding whether the fault is in the handle assembly, wiring, or control unit.
For more guided automotive diagnostics, visit STEP Diagnostics.
