What this code means
B0090 may indicate a no-signal condition from the left front impact sensor circuit.
What the vehicle may do
- The SRS warning indicator may turn on.
- The SRS system may store a fault related to the left front impact sensor signal.
- The restraint system may limit normal operation while the fault is present.
Possible fault areas
- Possible left front impact sensor issue.
- Possible connector or terminal issue in the sensor circuit.
- Possible wiring issue between the sensor and the SRS unit.
- Possible SRS unit control-side concern.
Diagnostic path
Open and safety setup
B0090 on this Accord points to a no-signal problem from the left front impact sensor circuit. In the bay, this may show up as an SRS warning indicator, and the SRS system may not be happy with the signal it is seeing from that front sensor area. The possible fault areas can include the left front impact sensor, the sensor connectors, the wiring between the sensor and the SRS unit, or less often the control side of the system. Before getting into the circuit checks, find out whether the vehicle has been in a collision. If it has, make sure the required SRS components were replaced with new correct-part-number components and were installed properly. Also handle this like any SRS diagnosis: follow SRS precautions, battery disconnect and reconnect precautions, and use the required SRS test equipment. This procedure calls for SRS Inflator Simulator 07SAZ-TB4011A and SRS Simulator Lead L 070AZ-SNAA300.
Verify the problem first
Start by proving the code is active. Clear the DTCs with the HDS, turn the vehicle to the ON mode, wait for 10 seconds, then check codes again with the HDS. If B0090-87 comes back, the failure is duplicated and you move into the connector checks. If it does not come back, treat it as an intermittent failure and do not force a hard-fault diagnosis that is not currently present. If other codes are present, check what they mean first instead of chasing this one in isolation.
Check the connector path
With the vehicle in OFF, check the connector connections in the left front impact sensor circuit. That includes SRS unit connector A, the 39P connector, the left front impact sensor 2P connector on the engine compartment wire harness, and the connector path between the SRS unit and the left front impact sensor. If the connectors are OK, continue to the circuit tests. If you find a poor connection, repair that connection, clear the DTCs, turn the vehicle back to ON, wait for 10 seconds, and recheck with the HDS. If B0090-87 is gone, the system is OK at that time. If it returns, continue with the wiring checks.
Check for a short between the sensor lines
Next, check whether the LFS plus and LFS minus lines are shorted together. Turn the vehicle to OFF, disconnect the negative cable from the 12 volt battery, and wait at least 3 minutes. Then disconnect SRS unit connector A, the 39P connector, and disconnect the left front impact sensor 2P connector on the engine compartment wire harness. Measure resistance between SRS unit connector A terminal No. 31 and terminal No. 32. You want an open circuit, or at least 1 MΩ. If it passes, those two wires are not shorted together and you go to the next short check. If it fails, the fault is a short to another wire in the engine compartment wire harness or dashboard wire harness, and the faulty harness is the repair path before clearing the DTC.
Check for a short to ground
Now check each LFS line for a short to ground. Keep the vehicle OFF, with SRS unit connector A disconnected and the left front impact sensor 2P connector disconnected. Measure from SRS unit connector A terminal No. 31 to body ground, and then from terminal No. 32 to body ground. Each check should show an open circuit, or at least 1 MΩ. If both pass, the LFS lines are not shorted to ground and you continue. If either one fails, the fault is a short to ground in the engine compartment wire harness or dashboard wire harness, and the faulty harness is the repair path before clearing the DTC.
Check for a short to power
Next, check for unwanted voltage on those same two lines. Reconnect the negative cable to the 12 volt battery, turn the vehicle to ON, and keep SRS unit connector A and the left front impact sensor 2P connector disconnected. Measure voltage from terminal No. 31 to body ground, and then from terminal No. 32 to body ground. The reading should be 0.2 V or less. If it passes, the LFS lines are not shorted to power and you move to the open-circuit check. If it fails, the fault is a short to power in the engine compartment wire harness or dashboard wire harness, and the faulty harness is the repair path before clearing the DTC.
Check for an open in the sensor 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 front impact sensor 2P connector on the engine compartment wire harness. With SRS unit connector A still disconnected, measure resistance between SRS unit connector A terminal No. 31 and terminal No. 32. The circuit should measure 1.0 Ω or less. If it does, the LFS plus and LFS minus wires are OK, and the next supported repair step is to replace the left front impact sensor, clear the DTC, and retest. If the code is still present after that, pause, recheck the earlier diagnostic path, and avoid guessing before making any SRS unit decision. Before replacing an SRS unit, check the SRS unit software version with the HDS; if it is not the latest version, update the software and retest. If the open-wire check does not measure 1.0 Ω or less, the fault is an open in the engine compartment wire harness or dashboard wire harness, and the faulty harness is the repair path before clearing the DTC.
Verify the repair
After the repair path is completed, clear the code and verify the repair by turning the vehicle ON and confirming the B0090 fault stays gone under the same basic check conditions. The takeaway is simple: prove the code first, inspect the connectors, then isolate the left front impact sensor circuit for shorts between the lines, shorts to ground, shorts to power, and opens before condemning the sensor or moving deeper into the SRS control side. For more diagnostic training, visit stepdiagnostics.com.
Final check
B0090 is often approached as an electrical circuit diagnosis: verify the fault, check connections, test the sensor wiring for shorts and opens, then verify the code stays gone.
For more guided automotive diagnostics, visit STEP Diagnostics.
