B1831 – Curtain shield airbag (right) squib circuit open (Toyota)

B1831 means the airbag system has a problem on the right curtain airbag circuit. In plain terms, the SRS warning light will stay on and the right-side curtain protection may not work in a crash. This is a Toyota manufacturer-specific code, so the exact logic can vary by platform. According to Toyota factory diagnostic data, this code indicates a “Curtain shield airbag (right) squib circuit open.” On a 2015 Toyota Auris, the SRS ECU sets B1831 when it cannot see the correct electrical load for the right curtain airbag igniter. Treat this as safety-critical and follow Toyota SRS depowering procedures before touching any related connector.

B1831 Quick Answer

B1831 on Toyota means the SRS ECU sees an open circuit in the right curtain shield airbag squib circuit. The airbag warning light stays on, and the right curtain airbag may not deploy.

What Does B1831 Mean?

Official definition: “Curtain shield airbag (right) squib circuit open.” The SRS ECU monitors the right curtain airbag igniter circuit. When it detects an open condition, it turns the SRS warning light on and stores B1831. In practice, the system cannot guarantee deployment for that airbag, so the ECU disables that part of the system to prevent unintended operation.

What the module is checking: The SRS ECU checks circuit continuity and expected resistance load through the right curtain squib loop. It does this through the harness, connectors, and any in-line safety components used on that Toyota platform. Why it matters: “Open” points you toward wiring, connectors, and terminal fit issues first. It does not prove the airbag or the ECU has failed. Use only OEM-approved SRS test methods and avoid probing squib circuits with standard meter leads.

Theory of Operation

Under normal conditions, the Toyota SRS ECU continuously monitors each airbag igniter circuit. The right curtain shield airbag contains a squib, which acts like an electrical igniter. The ECU expects to see a specific electrical load through the squib circuit. When the ECU commands deployment, it sends a controlled current through that circuit to ignite the squib.

With B1831, the ECU does not see the expected load on the right curtain squib circuit. A disconnected connector, damaged harness, backed-out terminal, or corrosion can break continuity. High resistance can also look like an open to the ECU. Because this circuit controls an explosive device, Toyota designs it to set a DTC quickly and lock on the warning lamp when monitoring fails.

Symptoms

You will usually notice an SRS warning first, then confirm the fault with a scan tool that can access Toyota SRS data.

• SRS light stays on in the instrument cluster
• Airbag message warning displayed, if equipped
• No readiness SRS system does not self-check to “normal” status
• Stored DTC B1831 present in SRS ECU memory
• Freeze frame code may log as current or history depending on connector movement
• Intermittent warning may change with seat position or body flex on rough roads
• Related codes other squib or side airbag circuit codes may appear if a shared connector area has issues

Common Causes

• Right curtain shield airbag squib connector not fully seated: A partially latched connector opens the squib circuit and the SRS ECU flags an open fault.
• High resistance from terminal fretting or corrosion: Oxidation at the squib-side or harness-side terminals raises resistance until the module interprets it as an open.
• Open in the right curtain airbag squib harness: A broken conductor inside the roof rail or A/C-pillar harness interrupts current flow during the ECU’s integrity check.
• Harness damage from trim work or water intrusion: Pinched wiring under headliner clips or moisture in the roof rail can cut or degrade the squib circuit.
• Improper prior SRS repair or non-OEM terminals: Incorrect terminal tension or wrong repair parts create intermittent opens that set the code at key-on.
• Connector lock, CPA, or secondary retainer missing: Without the lock, vibration can back terminals out and open the circuit.
• Faulty curtain shield airbag (right) inflator/squib unit: An internal open in the squib winding prevents the expected load from appearing to the SRS ECU.
• SRS ECU (airbag sensor assembly) connector issue: Bent pins, poor pin fit, or contamination at the ECU connector can open the monitored squib channel.

Diagnosis Steps

Use a scan tool with full Toyota SRS access, a DMM, and back-end voltage-drop test capability. Follow Toyota SRS depowering procedures before touching any SRS connector. Use only OEM-approved SRS test methods and adapters. Do not probe squib terminals with standard meter leads. Avoid ohmmeter checks across an airbag squib unless Toyota service information explicitly allows it.

1. Confirm DTC B1831 in the SRS ECU and record stored, pending, and history codes. Save freeze frame data if available. Focus on battery voltage, ignition state, and any related SRS DTCs. Freeze frame shows the conditions when the fault set. Use a scan tool snapshot later if you need to capture an intermittent open during wiggle testing.
2. Perform a fast visual inspection of the circuit path before any meter work. Inspect the right roof rail and A/C-pillar trim area for recent repairs, pinched headliner, water tracks, or disturbed harness routing. Check SRS-related fuses and power distribution next. Do not measure at the ECU first.
3. Verify SRS ECU power and ground integrity with voltage-drop testing under load. Keep the circuit operating as Toyota allows for the test. Measure ground drop at the ECU grounds while powered. Target less than 0.1 V drop. A clean continuity check cannot find a high-resistance ground.
4. Depower the SRS system using Toyota’s procedure and required wait time. Then disconnect the 12 V battery as specified. Confirm the system stays depowered. Never disconnect an SRS connector with the system powered.
5. Inspect the right curtain shield airbag squib connector and harness connector locks. Look for a missing CPA, broken secondary lock, or an unseated latch. Check for terminal push-out, bent pins, or signs of overheating. Correct any connector seating issues before deeper testing.
6. Inspect the SRS ECU connector condition on the squib channel for the right curtain airbag circuit. Look for spread terminals, contamination, or pin damage. Verify connector lever action and full lock engagement. Do not force connectors.
7. Perform harness integrity checks between the SRS ECU and the right curtain squib circuit using OEM-approved methods. Prefer a pin-to-pin resistance check of the harness only with both ends disconnected and the squib isolated. Do not measure through the airbag module. If Toyota service information calls for a dedicated SRS simulator or shorting bar verification, use that tool and procedure.
8. Check for intermittent opens with a controlled wiggle test of the roof rail harness and connector bodies. Keep the SRS system depowered while manipulating connectors. Use the scan tool after reassembly to observe whether B1831 returns immediately at key-on. A hard open in a continuously monitored circuit often returns right away.
9. If wiring and connectors pass, isolate the suspected component with Toyota-approved substitution testing. Use an OEM-approved SRS load tool or simulator in place of the right curtain squib if the service procedure permits it. This step helps separate a harness fault from an internal squib open without risking deployment.
10. After repairs, reassemble all connectors with locks installed and correct routing. Repower the SRS system per Toyota procedure. Clear SRS DTCs with the proper scan tool. Cycle the ignition and confirm B1831 stays cleared. Recheck for any companion SRS codes that may indicate a shared connector or power issue.

Professional tip: Treat B1831 as a suspected trouble area, not a confirmed bad airbag. Toyota SRS circuits use shorting bars and specific terminals that fool basic continuity tests. A connector that looks “plugged in” can still hold a backed-out terminal. Always verify connector lock position and terminal retention before condemning the curtain airbag.

Possible Fixes

• Reseat and secure the right curtain squib connector: Fully latch the connector and install or replace the secondary lock/CPA as required.
• Repair terminal fit issues: Correct terminal push-out, replace damaged terminals with OEM parts, and restore proper pin tension.
• Repair the open or high-resistance harness section: Restore wiring integrity in the roof rail/A-pillar area using Toyota-approved SRS wiring repair methods.
• Correct harness routing and trim interference: Remove pinch points, replace damaged clips, and protect the harness from sharp edges and water paths.
• Replace the right curtain shield airbag module only after circuit verification: Replace the airbag if tests confirm an internal squib open and the harness proves good.
• Service SRS ECU connector issues: Clean contamination, address pin damage, and ensure full connector lock engagement after verifying power and grounds.

Can I Still Drive With B1831?

You can usually drive a 2015 Toyota Auris with DTC B1831, but you should treat the SRS as compromised. This code means the SRS ECU sees an open circuit in the right curtain shield airbag squib circuit. That can disable that airbag and can affect how the SRS decides to deploy other airbags. The car will typically run and brake normally. However, crash protection may drop on the right side. Do not attempt DIY probing at SRS connectors. Follow Toyota depowering procedures before any inspection near the curtain airbag harness, headliner, A-pillar, or roof rail.

How Serious Is This Code?

B1831 is a safety-critical fault, not a drivability fault. In daily use, it may feel like an inconvenience because the airbag warning stays on. In a collision, it becomes serious because the right curtain shield airbag may not deploy. An “open” squib circuit often comes from wiring, connector, or terminal problems. It can also come from damage near the roof rail or pillar trim. SRS diagnosis requires OEM-approved methods and the right scan tool with full SRS access. Standard test lights and generic multimeters can trigger damage or unsafe conditions if used incorrectly.

Common Misdiagnoses

Technicians often replace the right curtain airbag first because the code names the squib. That wastes money when the real issue is a poor connection at an SRS connector, a backed-out terminal, or harness damage from trim work. Another common error involves probing SRS circuits with standard leads, which can spread terminals or set more codes. Some shops also clear codes and “see if it comes back.” That skips the key step: confirming the open using Toyota-approved check methods and verifying connector seating, CPA locks, and harness routing before touching any parts.

Most Likely Fix

The most common confirmed repair direction for B1831 involves correcting an intermittent or hard open in the right curtain squib circuit at a connector or harness segment. That usually means repairing terminal fit, corrosion, or a partially unseated connector after headliner or pillar trim work. Harness repair or replacement may follow if you find damaged wiring near the roof rail. Do not label the airbag module failed until you verify the circuit end-to-end using Toyota service information and approved SRS test procedures. After repair, confirm the SRS self-check passes and the DTC stays cleared during repeated key cycles and a road test under normal vibration.

Repair Costs

SRS/airbag repair costs vary significantly by component. Diagnosis must be performed by a qualified technician with SRS-capable equipment. Do not attempt airbag system repairs without proper training and safety procedures.

Last updated: April 3, 2026