What this code means
B0021 may indicate an open or increased resistance condition in the left side curtain airbag inflator circuit.
What the vehicle may do
- The SRS warning light may be on.
- The supplemental restraint system may limit normal operation while the fault is active.
- The code can be intermittent if it does not return during verification.
Possible fault areas
- The left side curtain airbag inflator connection may be involved.
- The floor wire harness may have a possible open circuit condition.
- The SRS unit connector or SRS unit may be involved.
- Prior collision repairs or incorrect SRS component installation can affect the diagnostic path.
Diagnostic path
Opening context
On this 2010 to 2016 Honda CR-V, B0021 points us toward a possible open or increased resistance condition in the left side curtain airbag inflator circuit. In the bay, the SRS light may be on, and the system may limit normal supplemental restraint operation while the fault is present. Broadly, this can involve the curtain airbag inflator connection, the floor wire harness, the SRS unit connection, or the SRS unit itself. Before diving in, find out whether the vehicle has been in a collision. If it has, make sure the required SRS components are correct, new where required, and properly installed before chasing the circuit.
Initial safety and setup
Treat this as SRS work from the start. Review the SRS handling precautions, the general troubleshooting approach, and the 12 volt battery terminal disconnect and reconnect process before touching connectors. Also keep one important point in mind for later: before replacing the SRS unit, check its software version with the HDS. If it is not the latest version, update the SRS unit software and retest before making that call.
Prove whether B0021-13 is current
Start by clearing the DTCs with the HDS. Turn the vehicle to the ON mode, wait for 10 seconds, then check for DTCs again with the HDS. If B0021-13 is indicated, the failure is duplicated and you keep going with the circuit check. If B0021-13 is not indicated, treat it as an intermittent failure; the system is OK at that moment. If another code is present, check what that code means first instead of forcing this path.
Check the left side curtain airbag inflator side
Next, turn the vehicle to the OFF (LOCK) mode. Disconnect the negative cable from the 12 volt battery, then wait at least 3 minutes. Remove the headliner, then disconnect the left side curtain airbag inflator 2P connector on the floor wire harness. At that floor wire harness connector, connect terminal No. 1 and terminal No. 2 together with a jumper wire. Reconnect the negative cable to the 12 volt battery, clear the DTCs with the HDS, turn the vehicle to the ON mode, wait for 10 seconds, and check for DTCs again. If B0021-13 is not indicated after this jumper check, the direction is a faulty left side curtain airbag inflator; replace the left side curtain airbag, then clear the DTC. If B0021-13 is still indicated, move on to checking the LCA plus and LCA minus wires for an open.
Check the LCA plus and LCA minus wires for an open
For the open-wire check, turn the vehicle back to the OFF (LOCK) mode. Disconnect the negative cable from the 12 volt battery and wait at least 3 minutes. Remove the jumper wire from the left side curtain airbag inflator 2P connector on the floor wire harness. Then disconnect SRS unit connector B, the 39P connector. At SRS unit connector B, connect terminal No. 1 and terminal No. 2 together with a jumper wire. Now measure resistance between the left side curtain airbag inflator 2P connector No. 1 and No. 2 on the floor wire harness. The decision point is 1.0 Ω or less.
Use the resistance result to choose the next move
If the resistance is not 1.0 Ω or less, the path points to an open in the floor wire harness. Replace the floor wire harness, then clear the DTC. If the resistance is 1.0 Ω or less, the LCA plus and LCA minus wires are OK. At that point, look closely at the SRS unit connector B connection and the SRS unit connection. If the connection is OK, follow the software check first; update and retest if the software is not current. If the connection is OK and the diagnostic path still points there, replace the SRS unit. If the DTC does not clear after that, the remaining direction is to replace the floor wire harness.
Takeaway
The key on B0021 is to keep the logic clean: first prove the fault is current, then bypass the curtain airbag inflator side, then check the LCA circuit back through the floor wire harness before blaming the SRS unit. Clear and recheck the code at the points called out, and do not skip the SRS unit connection and software checks before replacement. For more diagnostic training, visit stepdiagnostics.com.
Final check
This diagnosis often comes down to separating an inflator-side issue from an open in the LCA circuit and then checking the SRS unit connection and software before replacement decisions.
For more guided automotive diagnostics, visit STEP Diagnostics.
