What this code means
B1668 may mean the keyless access control unit is not seeing the rear shelf or rear interior LF antenna circuit as expected.
What the vehicle may do
- The keyless access system may operate intermittently or may not behave normally.
- One-push start or key detection behavior can be affected depending on when the system needs that antenna area.
Possible fault areas
- A possible rear interior LF antenna concern may be involved.
- Wiring or connector issues between the antenna and the keyless access control unit can be involved.
- The keyless access control unit side of the circuit may be involved.
Diagnostic path
Opening context
On this 2010 to 2015 Honda Civic with the 1.8 gas engine, B1668 points to a rear shelf LF antenna circuit open in the keyless access system. In plain language, the keyless access control unit may not be seeing that rear interior antenna circuit the way it expects. The vehicle may have keyless access or one-push start behavior that is intermittent or not operating normally, especially when the system is trying to use the rear antenna area. The possible fault areas are the rear interior LF antenna, the wiring and connector condition between that antenna and the keyless access control unit, or the control unit side of the circuit. The diagnostic path is straightforward: first prove the code is current, then check whether the control unit can drive the antenna circuit, and only then check the two wires for an open or high resistance.
Prove the code is current
Start with the basic system checks. Clear the DTCs with the HDS. From the ONE-PUSH START system menu, select the KEYLESS ACCESS CONTROL UNIT, enter SELF CHECK, run the self check, and then check for codes again. If B1668 is indicated, continue to the antenna circuit output check. If B1668 is not indicated, treat it as an intermittent failure. The system is OK at this time, so check for loose or poor connections before going any deeper.
Check the control unit output to the rear interior LF antenna
Next, check the EXT_TI plus and EXT_TI minus output from the keyless access control unit. Press the engine start/stop button to select OFF mode, then disconnect the rear interior LF antenna 2P connector. Press the engine start/stop button again to select ON mode. With the HDS, go into KEYLESS ACCESS CONTROL under the ONE-PUSH START system, enter FUNCTIONAL TESTS, and choose TRUNK/REAR SHELF ANTENNA L DC OUTPUT. Connect the voltmeter across the rear interior LF antenna 2P connector: test point 1 is terminal No. 1, the LT BLU wire, and test point 2 is terminal No. 2, the GRY wire. The decision here is whether there is voltage. If there is voltage, the path calls for replacing the rear interior LF antenna. If there is no voltage, move on to the open-wire check.
Check the EXT_TI circuit wiring for an open or high resistance
For the wire check, press the engine start/stop button to select OFF mode. Leave the rear interior LF antenna 2P connector disconnected, and disconnect keyless access control unit connector A, the 32P connector. Now check continuity on both antenna lines. For EXT_TI plus, check between keyless access control unit connector A 32P terminal No. 18, the PNK wire, and rear interior LF antenna 2P terminal No. 1, the LT BLU wire. For EXT_TI minus, check between keyless access control unit connector A 32P terminal No. 2, the PUR wire, and rear interior LF antenna 2P terminal No. 2, the GRY wire. If continuity is present, the EXT_TI plus and EXT_TI minus wires are OK, and the path calls for replacing the keyless access control unit. If continuity is not present, repair the open or high resistance in the wire.
Takeaway
The key on B1668 is not to guess at the antenna or the control unit. Confirm the code is current, check for output at the rear interior LF antenna connector, and then prove the two circuit wires before making the final call. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1668 is approached by confirming the code, checking control unit output at the antenna connector, and then checking the antenna circuit wiring before making the final decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
