What this code means
B1E77 can set when the right side BSI radar unit sees the indicator circuit voltage out of its normal range as the BSI alert indicator comes on or off.
B1E77 concerns the indicator circuit associated with the right side BSI radar unit. The unit monitors the indicator circuit voltage as the alert indicator comes on or off. An out-of-range voltage during that operation can cause the code to be stored.
The diagnostic path considers the alert indicator, its related paths and the radar unit. Those are distinct possibilities. The indicator test and the later circuit readings are used to decide which part of that path is implicated.
What the vehicle may do
- The BSI alert indicator comes on or off.
Possible fault areas
- The right BSI alert indicator may have a problem.
- The related circuit may have a problem.
- The right side BSI radar unit may have a problem.
Start with the confirmation condition. The indicator inspection then uses the specified disconnected connector and jumper connection, with an expected change from the original DTC to the stated comparison DTC.
After that result, the BSI_R_IND and GND paths are checked under the specified disconnected-connector and IG conditions. The radar-unit conclusion is a later decision that depends on the other inspection items being normal.
Diagnostic path
Understand the stored condition
On this 2025 Honda Accord 1.5 turbo, B1E77 is an open in the right side BSI radar unit indicator circuit. The BSI radar unit watches the indicator circuit voltage when the BSI alert indicator comes on or off. If that voltage is out of its normal range, the BSI radar unit stores this code. This check evaluates the component through its related components.
Confirmation Procedure
Start by turning the vehicle to the ON mode, then wait for at least 5 seconds. This is the confirmation step before moving into the indicator and circuit checks.
Right BSI Alert Indicator Inspection
For the right BSI alert indicator inspection, disconnect the right BSI alert indicator 2P connector. Then connect a jumper wire between terminals No. 1 and No. 2 of that connector. Turn the vehicle to the ON mode. The expected result is that DTC B1E77 changes to DTC B1E75. If this inspection is normal, there is a problem with the right BSI alert indicator. If it is abnormal, there is a problem with other related components.
The expected change in DTC is the result criterion for this particular test. Read it as the response to the specified test connection. That response is used to separate an indicator problem from other related components; it is not the same criterion as the resistance readings in the following wire inspections.
BSI_R_IND Open Wire Inspection
Next, prepare for the BSI_R_IND and GND open wire inspections. Leave the right BSI alert indicator 2P connector disconnected, and disconnect the right side BSI radar unit 6P connector. With IG Mode OFF, perform the BSI_R_IND open wire inspection. The expected result is less than 1 Ω. If this open wire inspection is abnormal, there is a problem in the circuit.
GND Open Wire Inspection
With the same connectors disconnected and IG Mode OFF, perform the GND open wire inspection. The expected result is less than 1 Ω. If this inspection is abnormal, there is a problem in the circuit.
Right Side BSI Radar Unit Inspection
After the related inspections are completed, use the remaining result for the right side BSI radar unit. If the other inspection items indicated a normal condition, then it is determined that the remaining right side BSI radar unit is the cause. In that case, the expected finding is that there is a problem with the right side BSI radar unit.
Visual Reference Note
This diagnostic check evaluates the component through its related components.
Closing Takeaway
The key is to prove whether the indicator responds to the jumper check, then verify the BSI_R_IND and GND paths before judging the right side BSI radar unit.
Final check
Check the indicator response and related circuit paths before judging the right side BSI radar unit.
Retain the DTC response from the indicator test alongside the BSI_R_IND and GND results. Together, they explain why the procedure points to the indicator, a circuit path or, conditionally, the right side BSI radar unit.
