What this code means
B0091 may indicate that the SRS unit is not receiving the expected signal from the left side impact sensor circuit.
What the vehicle may do
- The SRS warning may be displayed.
- The code may be current or intermittent.
- The restraint system may limit normal operation while the fault is active.
Possible fault areas
- A possible issue with the left side impact sensor signal path.
- A possible wiring or connector concern in the floor harness between the sensor and the SRS unit.
- A possible short, open, or power/ground-related circuit fault.
- A possible SRS unit software or module concern after circuit checks pass.
Diagnostic path
Opening
On this 2010 to 2016 Honda CR-V with the 2.4 gas engine, B0091 is an SRS fault for a no-signal condition from the left side impact sensor circuit. In plain terms, the SRS unit may not be seeing the signal it expects from that left side impact sensor path. The driver may see an SRS warning, and the system may store the code as a current or intermittent fault. Broadly, this can involve the side impact sensor, the floor harness and connectors between the sensor and the SRS unit, possible shorts or opens in the LS1 lines, or an SRS unit software or module issue. We’re going to work through it in order, without guessing.
Safety and pre-checks
Before getting into the circuit checks, handle this like any SRS job. Find out whether the vehicle was in a collision. If it was, confirm the required SRS components were replaced with new parts of the correct part number and that they were installed correctly. Use normal SRS precautions, including the proper 12 volt battery disconnect and reconnect process. Also, keep the SRS unit software note in mind: before condemning the SRS unit later in the path, check its software version with the HDS. If it is not current, update it and retest before replacing the unit.
Confirm the code state first
Start by clearing the DTCs with the HDS. Turn the vehicle to the ON mode, wait for 10 seconds, and then check for DTCs again. If only B0091-87 comes back, continue into the circuit checks. If it comes back with the paired left side impact sensor fault, the path calls for replacing the left side impact sensor first, then clearing the DTC. If no DTC comes back, treat it as an intermittent condition and the system is OK at that moment. If other codes are present, check what they mean first instead of forcing this test path.
Check for a short between the LS1 lines
Now check whether the two LS1 wires are shorted together. Turn the vehicle to OFF, disconnect the negative cable from the 12 volt battery, and wait at least 3 minutes. Disconnect SRS unit connector B, the 39P connector, and disconnect the left side impact sensor first 4P connector at the floor wire harness. Measure resistance between SRS unit connector B terminal No. 28 and terminal No. 29. You want an open circuit, or at least 1 MΩ. If that reading is good, the two wires are not shorted together, so move on. If it fails, the fault path is a short to another wire in the floor wire harness between the SRS unit and the left side impact sensor, and the floor wire harness replacement path applies, followed by clearing the DTC.
Check for a short to ground
With the SRS unit connector and the left side impact sensor connector still disconnected, check each LS1 line to ground. Measure from SRS unit connector B terminal No. 28 to body ground, and then from terminal No. 29 to body ground. Again, you’re looking for an open circuit, or at least 1 MΩ. If both checks pass, the LS1 lines are not shorted to ground, so continue. If either check fails, the path identifies a short to ground in the floor wire harness between the SRS unit and the left side impact sensor. In that case, replace the floor wire harness and clear the DTC.
Check for a short to power
Next, reconnect the negative cable to the 12 volt battery and turn the vehicle to the ON mode. Leave SRS unit connector B and the left side impact sensor connector disconnected for this check. Measure voltage from terminal No. 28 to body ground, and then from terminal No. 29 to body ground. The result should be 0.2 V or less. If both lines are at or below that value, they are not shorted to power, so go to the open-circuit check. If the voltage is higher, the path identifies a short to power in the floor wire harness between the SRS unit and the left side impact sensor. Replace the floor wire harness and clear the DTC.
Check for an open in the LS1 circuit
For the open-wire check, turn the vehicle back to OFF. Connect the black terminal of SRS simulator lead L to the SRS inflator simulator jumper connector, then connect SRS simulator lead L to the left side impact sensor first 4P connector on the floor wire harness. Now measure resistance between SRS unit connector B terminal No. 28 and terminal No. 29. The expected result is 1.0 Ω or less. If the circuit passes, the LS1 wiring is considered OK. At that point, replace the left side impact sensor, clear the DTC, and retest. If the DTC remains after that, check the SRS unit software version with the HDS before going any further. If the software is not the latest, update it and retest. If the code is still present after that path, replace the SRS unit. If the open-wire check does not meet 1.0 Ω or less, the fault path is an open in the floor wire harness between the SRS unit and the left side impact sensor. Replace the floor wire harness and clear the DTC.
Verification and takeaway
After the indicated repair, keep verification separate from the circuit testing. Clear the DTCs, run the system again, and confirm B0091 does not return under the same check conditions. The takeaway is simple: prove the LS1 circuit first — short between wires, short to ground, short to power, then open circuit — and only move to the sensor or SRS unit after the harness path passes. For more diagnostic training, visit stepdiagnostics.com.
Final check
B0091 is often diagnosed by proving the sensor circuit first, then moving to the sensor and SRS unit only after the wiring checks pass.
For more guided automotive diagnostics, visit STEP Diagnostics.
