B1806 – P squib circuit open (Toyota)

B1806 means the airbag system has detected an open circuit in a squib circuit. In plain terms, your Toyota Auris may not deploy one of its airbags as designed. You will almost always see the SRS/airbag warning lamp stay on. According to Toyota factory diagnostic data, this code indicates “P squib circuit open.” This is a Toyota manufacturer-specific definition. The exact component naming behind “P squib” can vary by platform and restraint layout. Treat the code as a pointer to a suspected circuit problem, not a confirmed bad airbag part. Follow Toyota SRS depowering procedures before touching any related connector.

B1806 Quick Answer

B1806 on Toyota means the SRS ECU sees an open in the “P squib” deployment circuit. The SRS warning lamp stays on and that circuit’s restraint function may disable until you restore proper circuit continuity and clear the code with an SRS-capable scan tool.

What Does B1806 Mean?

Official definition: “P squib circuit open.” The SRS ECU detected that the squib circuit it labels as “P” does not look electrically complete. In practice, the system flags a fault and may inhibit deployment for that circuit to prevent an unintended event.

What the module checks and why it matters: The SRS ECU continuously monitors the squib loop with an internal diagnostic method. It expects the circuit to stay within a valid continuity window. An open circuit occurs when wiring, connectors, or the squib path breaks electrically. That matters because you must confirm the harness and connector integrity first. Do not replace an airbag, pretensioner, or spiral cable until you verify the circuit with OEM-approved SRS test procedures.

Theory of Operation

Under normal conditions, the Toyota SRS ECU monitors each squib circuit as a dedicated two-wire loop. The loop runs from the ECU through the harness and connectors to the squib device. The ECU uses internal diagnostics to confirm the loop stays intact during key-on and operation.

B1806 sets when the ECU’s continuity check for the “P squib” loop indicates an open circuit. A poor connection can mimic an open. Corrosion, connector damage, an unlocked shorting bar connector, or harness strain can break continuity. Incorrect testing can also create problems. Standard test lights and common ohmmeters can trigger SRS faults or damage components. Use only Toyota-approved methods and always depower the SRS before disconnecting related connectors.

Symptoms

These are the most common signs you will notice with B1806 on a Toyota Auris.

• SRS warning lamp stays on or returns immediately after key-on self-check.
• No readiness for that circuit as the ECU disables the affected squib output logic.
• Stored SRS DTC B1806 in the SRS ECU, not in the engine ECU.
• Failed inspection due to an illuminated airbag warning lamp.
• Intermittent light if a connector momentarily opens with seat movement or vibration.
• Additional SRS codes if the same harness branch feeds multiple restraint components.
• Scan tool data clue freeze frame or sub-status may show current versus history, depending on tool capability.

Common Causes

• Disengaged or damaged squib connector: A partially seated connector at the P squib increases resistance or opens the circuit, so the SRS ECU flags an open fault.
• Harness open between SRS ECU and the P squib: A broken conductor inside the airbag harness interrupts the deployment loop, which matches the “circuit open” detection logic.
• Terminal spread or poor pin fit: Loose terminal tension creates an intermittent open that often returns immediately at key-on during the SRS self-check.
• Corrosion or contamination at SRS connectors: Oxidation raises contact resistance until the ECU interprets the loop as open, especially after moisture intrusion.
• Damage at a seat/b-pillar/steering column harness routing point: Normal Toyota routing varies by platform, but pinch points and movement areas commonly stress SRS wiring and cause opens.
• Aftermarket accessory installation damage: Poorly routed audio, alarm, or remote-start wiring can nick or pull the SRS harness, opening the squib circuit.
• Wrong component or connector mated after prior repair: A mismatched connector body, incorrect terminal, or incompatible part can prevent full engagement and leave the circuit open.
• Clock spring/spiral cable fault (if the P squib is in the steering wheel path): If the monitored P squib path routes through the spiral cable on this Auris, an internal open can break the circuit as the wheel turns.
• Fault within the squib or airbag module assembly: An internal open in the initiator or internal lead can present as an open circuit, but you must prove wiring integrity first.

Diagnosis Steps

Use a scan tool with full Toyota SRS access, plus OEM service information for connector IDs and depowering steps. Have a DMM and back-probing tools approved for SRS work. Do not use a test light. Do not probe SRS connectors with standard leads. Use only Toyota-approved methods and any specified simulators.

1. Connect a capable scan tool and run a full SRS health check. Record B1806 status as pending, stored, or history. Save freeze frame data if the tool provides it. Focus on battery voltage, ignition state, and any companion SRS DTCs that indicate the same circuit family. Freeze frame shows conditions when the fault set. A scan tool snapshot, triggered during a wiggle test, captures intermittent opens during diagnosis.
2. Perform SRS-safe prep before any physical checks near the squib circuit. Depower the SRS system using Toyota procedures and wait the specified time for reserve energy to discharge. Next, do a visual inspection of the suspected circuit path and related connectors before any meter work. Look for disturbed trim, signs of prior collision repair, and harness pinch points that match Auris routing.
3. Check fuses and power distribution that feed the SRS ECU and any related junction connectors. Verify each fuse supplies power on the correct side under load, not just continuity. A weak fuse contact can drop voltage during self-check. Restore any missing power feed before deeper circuit testing.
4. Verify SRS ECU power and ground integrity with voltage-drop testing under load. Turn ignition ON and command the system awake per scan tool capability. Load the circuit using normal module operation, then measure ground voltage drop. Keep ground drop under 0.1V with the circuit operating. Also check power feed drop across the feed path. Do not rely on unloaded voltage readings.
5. Identify what Toyota defines as the “P squib” on this 2015 Auris using service information. Toyota naming can vary by platform and restraint design. Confirm the exact component and connector locations before touching parts. This step prevents swapping the wrong airbag or inspecting the wrong harness leg.
6. With SRS depowered per Toyota procedure, inspect the P squib connector and the SRS ECU-side connector for terminal damage. Look for pushed-out pins, terminal spread, corrosion, and incomplete latch engagement. Confirm CPA locks or secondary locks fully seat, if equipped. Correct any connector issues found, then reassemble using proper connector handling rules.
7. Check the harness for an open using an OEM-approved method. Do not measure resistance directly through a live squib unless Toyota service information explicitly allows it. Use the specified breakout leads, shorting bars behavior checks, or an approved airbag simulator where required. If the platform calls for checking continuity between specific ECU pins and the squib connector, do it with connectors disconnected and SRS depowered. Move the harness during the test to find intermittent opens.
8. If Toyota procedures allow, perform a harness-side integrity test with a known-good simulator in place of the squib. This isolates the vehicle wiring and ECU monitoring from the airbag module. If B1806 changes behavior with the simulator installed, you narrowed the fault to the component side. If B1806 remains, focus on wiring, terminals, and ECU connector integrity.
9. Inspect any moving interface in the circuit path that could open with motion. On many Toyota layouts, the steering wheel path uses a spiral cable. Seat-mounted airbags route through seat harness connectors that move. Confirm the exact path for the Auris and perform a controlled wiggle test while monitoring SRS data. Use a scan tool snapshot to capture the moment the fault flips from normal to open.
10. After repairs, re-enable the SRS system using Toyota procedures. Clear SRS DTCs with the scan tool, then run the SRS self-check. Verify the warning lamp proves out and stays off. Re-scan to confirm B1806 does not return as a current or pending code. If the code returns immediately at key-on, treat it as a hard fault and re-check connector seating and open-circuit test results.

Professional tip: Treat B1806 as a loop-integrity fault first, not a parts failure. Most repeat comebacks come from terminal tension issues or an unseated secondary lock. Use voltage-drop for feeds and grounds, then isolate the loop with Toyota-approved tools. Avoid “continuity only” checks, because high resistance and intermittent opens can pass at rest.

Possible Fixes

• Reseat and secure the P squib connector: Restore positive engagement, confirm locks, and correct any pin alignment issues found during inspection.
• Repair an open in the harness: Fix broken conductors, chafed sections, or damaged routing using Toyota-approved repair methods for SRS wiring.
• Terminal repair at the affected connector: Replace spread, corroded, or loose terminals and connector bodies as required, then verify retention and pin fit.
• Correct power or ground distribution faults feeding the SRS ECU: Repair high-resistance fuse contacts, grounds, or junction connector issues confirmed by voltage-drop testing.
• Replace the spiral cable/clock spring only after isolation testing confirms it: If the P squib path routes through it and testing proves an internal open, replace and re-verify.
• Replace the airbag/squib component only after wiring checks pass: If an approved simulator test or OEM flow chart isolates an internal open, replace the confirmed failed unit and clear codes.

Can I Still Drive With B1806?

You can usually drive the vehicle, but you should not treat it as “safe.” Toyota DTC B1806 (P squib circuit open) indicates the SRS ECU sees an open circuit in a squib circuit. That means the restraint system may not fire that device when needed. In some Toyota designs, the ECU may also disable other SRS outputs as a fail-safe. Do not attempt DIY testing at the connectors. Do not probe SRS circuits with standard meter leads. Park the vehicle, keep occupants to a minimum, and schedule diagnosis with a shop that has full SRS scan-tool access and follows Toyota depowering procedures before touching any SRS wiring.

How Serious Is This Code?

This code is safety-critical, not a drivability fault. Your 2015 Toyota Auris will typically start and drive normally, so it can feel like an inconvenience. However, the SRS should be treated as potentially compromised until proven otherwise. An “open” squib circuit often results from high resistance, a loose connector, harness damage, or an incorrect component connection. Any of those can prevent proper deployment during a crash. Proper diagnosis requires SRS-capable equipment, correct depowering steps, and OEM-approved test methods. If you lack SRS training and the correct tools, do not attempt repairs. A mistake can trigger deployment or leave the system unsafe.

Common Misdiagnoses

Technicians often replace an airbag module or the clock spring too early because “squib open” sounds like a failed component. That wastes money and can add new faults if connectors do not seat correctly. Another common error involves back-probing SRS connectors with standard meter probes. That can spread terminals or damage shorting bars. Shops also misread “open” as a broken wire every time. On Toyotas, connector tension, corrosion from past interior work, or an improperly latched SRS connector can create an intermittent open. Avoid guesswork. Confirm the affected circuit and connector location with a Toyota-capable scan tool, then verify the wiring path and terminal fit using approved methods only.

Most Likely Fix

The most common confirmed repair directions for B1806 involve restoring circuit continuity at a known trouble spot, not replacing the SRS ECU. Start with the P squib connector path identified in Toyota service information. A technician typically finds an unseated connector, poor terminal contact, or harness damage near a moving or recently serviced area. After correct depowering, they inspect for backed-out terminals, bent pins, and connector locks that did not fully engage. If inspection proves the wiring fault, repair or replace the affected sub-harness or connector pigtail using OEM procedures. Then confirm the fix by rechecking SRS DTC status and running the ECU’s self-check; do not “clear and send.”

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