What this code means
B1E77 may mean the right side blind spot information alert indicator circuit is open or not responding electrically the way the right side radar unit expects.
What the vehicle may do
- The right side blind spot alert indicator may not operate normally.
- The blind spot information system may store a fault even if the symptom is intermittent.
- The driver may see a blind spot system warning or notice reduced alert function.
Possible fault areas
- Possible right BSI alert indicator issue.
- Possible open, high resistance, or poor connection in the indicator circuit.
- Possible ground-side circuit issue.
- Possible right side BSI radar unit issue after the related circuit checks are normal.
Diagnostic path
Code overview
On this Civic, B1E77 points to an open condition in the right side BSI radar unit indicator circuit. In plain terms, the radar unit may not be seeing the indicator circuit voltage it expects when the right BSI alert indicator is commanded on or off. The driver may notice the blind spot alert indicator on that side not acting normally, or the system may store the code without an obvious symptom. The fault area can be the right BSI alert indicator, the indicator circuit wiring or ground side, connector issues, or the right side BSI radar unit itself. Start with the basic system checks and follow a structured diagnostic approach before getting into pinpoint testing.
Confirm the fault condition
To confirm the code path, turn the vehicle to the ON mode and wait for at least 5 seconds. That gives the BSI radar unit time to run the check. If other codes are present, check what they mean first, but keep this diagnosis focused on B1E77 and the right side indicator circuit.
Check the right BSI alert indicator path
Next, check the right BSI alert indicator circuit. Disconnect the right BSI alert indicator 2P connector. Then connect terminals No. 1 and No. 2 of that connector with a jumper wire. Turn the vehicle to the ON mode. A normal response is that B1E77 changes to the related opposite-condition code. Since there is no direct standalone test for the indicator itself, this step uses the related circuit behavior to separate an indicator problem from the rest of the circuit. If the response is normal, the problem is with the right BSI alert indicator. If the response is abnormal, continue into the related circuit checks.
Check the BSI_R_IND and ground circuits for an open
For the open-wire inspection, disconnect the right BSI alert indicator 2P connector, then disconnect the right side BSI radar unit 6P connector. With IG Mode OFF, check the BSI_R_IND circuit. The normal condition is less than 1 Ω. Then check the ground circuit the same way, also with IG Mode OFF. The normal condition there is also less than 1 Ω. If either check is abnormal, treat it as a circuit problem and stay in the wiring, connector, or ground side of the diagnosis.
Evaluate the remaining fault area
If the alert indicator check and the open-wire checks all show normal results, the remaining fault area is the right side BSI radar unit. At that point, do not keep chasing the indicator or the harness without a reason; the diagnostic path has narrowed the problem to the radar unit side.
Wrap-up
The key on B1E77 is to prove the indicator response first, then prove the BSI_R_IND and ground circuits are not open. If those checks pass, the remaining suspect is the right side BSI radar unit. After the fault is corrected, rerun the ON-mode confirmation and make sure B1E77 stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
Diagnose B1E77 by confirming the code, simulating the indicator circuit response, checking the indicator and ground circuits for an open, and only then considering the right side BSI radar unit as the
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