What this code means
B1668 may indicate an open circuit concern in the rear shelf LF antenna circuit for the keyless access system.
What the vehicle may do
- Keyless access operation may be inconsistent.
- The system may store the code during a self-check even if the concern is intermittent.
Possible fault areas
- Rear shelf LF antenna circuit
- Possible open or high resistance in the EXT M plus or EXT M minus wiring
- Possible loose, poor, or damaged connector contact
- Possible rear shelf LF antenna or keyless access control unit involvement
Diagnostic path
Code overview
On this Accord, B1668 may indicate an open circuit concern in the rear shelf LF antenna circuit for the keyless access system. In plain terms, the control unit may not be seeing the rear antenna circuit the way it expects to. The customer may notice keyless access functions acting inconsistently, or the system may simply store the code during a self-check. The possible areas to keep in mind are the rear shelf LF antenna circuit, the EXT M plus and EXT M minus wiring between the antenna and the keyless access control unit, connector fit and terminal condition, and possible control unit involvement.
Start by verifying the code
Start with the basic system checks. Clear the DTCs with the HDS, go into the mode menu, enter self check, run the self check, and then check codes again. If B1668 comes right back, continue into circuit testing. If it does not return, treat it as an intermittent at this time. The system is okay right now, so concentrate on loose connections, poor terminal contact, or anything disturbed around the rear antenna circuit.
Check control unit output on the antenna lines
Next, check whether the keyless access control unit can drive the rear antenna circuit. Put the vehicle in OFF mode with the engine start/stop button, then disconnect the rear shelf LF antenna 2P connector. Put the vehicle back in ON mode. On the HDS, select Keyless Access Control from the one-push start system menu, go into functional tests, and set up the trunk room antenna test. Connect the voltmeter across the two antenna connector terminals: terminal No. 1 is the WHT wire, and terminal No. 2 is the LT GRN wire. Run the trunk room antenna test and look for voltage. If voltage is present, the circuit driver is producing output and the diagnostic path calls for replacing the rear shelf LF antenna. If there is no voltage, keep going and check the wiring for an open.
Check the EXT M plus and EXT M minus wires for an open
For the open-wire check, put the vehicle back in OFF mode. Disconnect keyless access control unit connector A, the 32P connector, and leave the rear shelf LF antenna 2P connector disconnected. Check continuity on both sides of the antenna circuit. For the EXT M plus line, check between keyless access control unit connector A, terminal No. 18, WHT wire, and the rear shelf LF antenna 2P connector terminal No. 1, WHT wire. For the EXT M minus line, check between keyless access control unit connector A, terminal No. 2, LT GRN wire, and the rear antenna 2P connector terminal No. 2, LT GRN wire. If both lines 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 affected wire.
Verify the repair
Once the called-out repair is made, keep verification separate from the circuit test. Use the same HDS clear-and-self-check routine to confirm B1668 stays gone. The takeaway is simple: prove the code is current, prove whether the control unit can output on the antenna lines, then prove the two wires before condemning a component. For more diagnostic training, visit stepdiagnostics.com.
Final check
Prove the code is current, check output, then check circuit continuity before making the repair decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
