B1831: Curtain Squib RH Open

Circuit fault

What B1831 means

The curtain shield airbag runs along the roof rail above the passenger side windows, and its squib is fired through a circuit that travels up the pillar to reach it. The ECU sends a small test current down that path and measures the return. An open reading means the current found no complete path at all, which is what B1831 records.

Curtain wiring runs through areas that get opened up more than people realize. Headliner work, pillar trim removal, roof rack installs, and water leaks at the windshield or sunroof drains all put that circuit at risk. The connector at the curtain itself is a frequent finding, since it gets disturbed whenever the headliner comes down.

Common causes

• A curtain airbag connector at the roof rail left unplugged or unlatched after headliner work
• A broken wire in the pillar where the harness bends or was pinched by trim
• Corroded pins from water leaking at the windshield, sunroof drain, or door seal
• An inflator in the curtain that has failed open internally
• A backed out terminal at the ECU connector on the curtain circuit
• Damage from roof rack, antenna, or accessory installation through the roof structure

Crash data or hardware fault?

What the module has here is a live resistance measurement instead of a crash record. The ECU tests the curtain loop on every key cycle, so the code clears itself once continuity is restored and the system passes startup. Crash data is the permanent entry made when airbags deploy, which stays in the module until a reset removes it.

Does our reset clear it?

Bench work on the module will not close an open circuit. The ECU measures the curtain loop again at the next key on and stores B1831 right back. Repair the connector or the wiring first and verify the loop reads in range. If the curtain has already deployed and the module carries that stored record, mailing the module to us is what clears that part after the repairs.

Which makes throw it

Toyota uses B1831 for an open in the right hand curtain shield squib circuit. Toyota labels the roof mounted side airbag a curtain shield airbag, so parts listings and repair information may use that longer name.

What to do next

Drop the right side pillar trim and check the curtain connector before you order anything, since a plug left unlatched after headliner or trim work is the most common cause. Look for water staining in the pillar while it is open. Measure the loop at the ECU connector to decide whether the break is in the harness or the curtain. We sell genuine OEM Toyota curtain airbags and can confirm the right part by VIN at 501-988-0611. Related codes: B1826, B1861, B1395.