B1651 – Knee airbag (driver) squib circuit open (Lexus)

B1651 means the driver knee airbag circuit has an open fault on your Lexus, so the SRS may not protect you as designed in a crash. In real use, you will usually see the airbag warning light, and the system may disable that airbag stage. According to Lexus factory diagnostic data, this manufacturer-specific code indicates a “Knee airbag (driver) squib circuit open.” This is not a universal SAE definition. Lexus can apply the same code number differently on other platforms, so always diagnose using the scan tool description for the vehicle you are working on. Treat this as safety-critical and follow Lexus SRS depowering procedures before touching any connector.

B1651 Quick Answer

B1651 on a Lexus points to an open circuit in the driver knee airbag squib circuit. The most common confirmed causes are a poor connection, harness damage, or an incorrect or disturbed SRS connector at the knee airbag.

What Does B1651 Mean?

Official meaning (Lexus): “Knee airbag (driver) squib circuit open.” In plain terms, the SRS ECU sees a break in the electrical path to the driver knee airbag igniter. That matters because the knee airbag may not deploy when commanded, and the SRS warning light will stay on until you repair the fault and clear codes with an SRS-capable scan tool.

What the module checks: The SRS ECU monitors the knee airbag squib circuit for continuity and a valid electrical load. An “open” sets when the ECU cannot see the expected circuit path through the squib and wiring. Why it matters for diagnosis: The code only identifies a suspected trouble area. You must confirm the open occurs in the harness, connector, or airbag module side using OEM-approved SRS test methods. Never “ohm” an airbag igniter with a standard meter.

Theory of Operation

Under normal conditions, the Lexus SRS ECU supplies a monitored circuit to each airbag squib. The ECU continuously verifies circuit integrity. It does this so it can deploy the correct airbags and log accurate faults.

When the driver knee airbag squib circuit goes open, current cannot flow through the monitored path. The ECU interprets that as a continuity loss. Common reasons include a partially unseated connector, terminal spread, corrosion, or harness damage near the knee bolster area. Any work around the steering column, lower dash, or knee panel can also disturb SRS connectors.

Symptoms

You will usually notice an SRS warning first, then scan tool confirmation.

• Airbag light SRS/AIRBAG warning lamp stays on
• Message warning message in the cluster on some Lexus configurations
• Disabled protection knee airbag may be inhibited until the fault is corrected
• Stored DTC B1651 stored in the SRS ECU memory
• Freeze frame event data showing when the circuit failed (scan tool dependent)
• Intermittent behavior light may flicker with steering column or lower dash movement if a connector is loose
• Failed self-check SRS lamp does not turn off after the normal bulb check

Common Causes

• Disconnected knee airbag squib connector: A partially latched or unplugged connector opens the driver knee airbag igniter circuit and the SRS ECU flags an open.
• High resistance from terminal fretting or corrosion: Oxidation or micro-movement at the terminals raises resistance until the SRS ECU interprets the circuit as open.
• Damaged harness at the driver knee area: A pinched, stretched, or cut wire near the lower dash or steering column can break conductor strands and create an intermittent open.
• Previous interior work left the SRS connector compromised: Trim, column, or lower dash service can leave a CPA lock unsecured or a terminal backed out.
• Incorrect aftermarket hardware or fastener interference: Non-OE brackets, screws, or accessories can chafe the SRS harness and open the squib circuit over time.
• Open circuit in SRS ECU to knee airbag wiring: A break in either squib lead between the SRS ECU and the knee airbag prevents the ECU from seeing the expected load.
• Connector damage from improper probing: Standard meter leads or test lights can spread terminals, causing a poor fit that later becomes an open circuit.
• Faulty knee airbag module (squib) internal connection: An internal open in the knee airbag inflator circuit can mimic harness damage, but you must verify wiring first.

Diagnosis Steps

Use a scan tool with full Lexus SRS access, OEM service information, and OEM-approved SRS test adapters. Gather a DMM for power and ground voltage-drop checks, plus lighting and mirror tools for close connector inspection. Follow Lexus SRS depowering procedures before touching any yellow SRS connector. Do not probe squib pins with standard leads or apply power.

1. Confirm DTC B1651 in the SRS system with a capable scan tool. Record stored vs current status and any related SRS codes. Save freeze frame data, focusing on battery voltage, ignition state, and the moment the ECU first logged the open circuit. Freeze frame shows conditions when the fault set, while a scan tool snapshot helps you capture an intermittent open during a wiggle test.
2. Perform a careful visual inspection of the circuit path before any meter work. Check the driver knee area harness routing, lower dash trim interference, and any recent repair signs. Look for pinched loom, rubbed tape, or strained connectors near the knee airbag and steering column area. Stop and depower the SRS system before you touch or unplug SRS connectors.
3. Check fuses and power distribution that feed the SRS system using service information. Verify fuse integrity and tight fit in the fuse block. Do not assume a fuse is good by sight alone. A poor fuse contact can drop voltage under load and create false SRS faults.
4. Verify SRS ECU power and ground with voltage-drop testing under load. Backprobe at approved points per Lexus procedures, not at squib circuits. With the circuit operating, measure ground drop and confirm it stays under 0.1V. Also confirm power feed drop stays low during key-on and during any self-test activity.
5. Depower the SRS system using Lexus OEM steps and the specified wait time. Then disconnect the knee airbag squib connector and the corresponding harness connectors called out in service information. Inspect connector bodies, CPA locks, secondary locks, and terminal alignment. Look for pushed-back terminals, spread tangs, water intrusion, or contamination.
6. Check the harness side for continuity and shorts using only OEM-approved methods. Do not measure resistance directly across a live squib or apply meter current into an inflator circuit. Use the Lexus-approved airbag simulator or specified test adapter where applicable. Verify each squib lead from the SRS ECU side to the knee airbag connector for an open, and check for short-to-ground or short-to-power conditions.
7. Perform a controlled wiggle test on the harness while monitoring SRS data and DTC status. Focus movement on known rub points near the lower dash, steering column brackets, and harness retainers. Use a scan tool snapshot to capture the exact moment the circuit status changes, if it flickers. If the code returns immediately at key-on, treat it as a hard open and prioritize connector and terminal integrity.
8. Inspect for evidence of non-OE accessories or prior trim repairs that contact the harness. Check for screws that protrude into the harness path and missing retainers that let the harness move. Repair routing and protection before you judge component condition.
9. If wiring and connector tests pass with OEM-approved tools, follow Lexus service information to isolate the knee airbag module from the vehicle harness. Use the approved simulator in place of the knee airbag, if specified for this platform. If the simulator stabilizes the circuit and B1651 does not reset, the fault points toward the knee airbag module or its connector interface, not the ECU.
10. After repairs, reassemble connectors with locks fully seated and restore proper harness routing. Re-enable the SRS system per Lexus procedures. Clear SRS DTCs with a capable scan tool, then cycle ignition and confirm B1651 stays cleared. Verify the SRS warning lamp proves out normally and recheck for pending or history SRS codes.

Professional tip: Treat B1651 as a “suspected open” in the driver knee airbag squib circuit, not a confirmed bad airbag. Most repeat comebacks come from terminal fit issues that pass a quick continuity check. Use voltage-drop principles on SRS feeds and use only Lexus-approved squib circuit test methods. A hard open usually returns immediately at key-on after you clear codes, so you can confirm repairs without a road test.

Possible Fixes

• Reseat and lock the knee airbag squib connector: Correct a partially engaged connector and confirm the CPA/secondary lock fully latches.
• Repair terminal fit or replace affected connector housing/terminals: Restore proper terminal tension and engagement when fretting, corrosion, or spread terminals cause an open.
• Repair or replace the damaged harness section: Fix broken conductors, chafed wiring, or pinched loom, then reroute and resecure the harness away from rub points.
• Correct power/ground distribution faults to the SRS system: Replace a poor fuse contact, repair a loose ground point, or correct a high-resistance splice verified by voltage-drop testing.
• Remove interference from prior repairs or accessories: Eliminate fasteners or brackets that contact the SRS harness and reinstall missing retainers and protective sheathing.
• Replace the driver knee airbag module only after circuit proof: Replace the knee airbag assembly when an OEM-approved simulator test and wiring checks isolate an internal open.

Can I Still Drive With B1651?

You can usually drive a Lexus RX400h with B1651, but you should treat the SRS system as compromised. This code points to an open circuit in the driver knee airbag squib circuit. That means the SRS ECU may disable that airbag stage and may limit related deployment logic. The vehicle will drive normally, but crash protection may not work as designed. Do not attempt DIY probing or connector checks around the knee airbag area. Follow Lexus SRS depowering procedures before any work near yellow connectors or the lower dash. Schedule professional diagnosis as soon as possible.

How Serious Is This Code?

This code is serious because it involves a squib circuit, which is the deployment path for an airbag. In normal driving, you may notice no change except an SRS warning light. In a collision, the driver knee airbag may not deploy, or the system may change how it manages other restraints. Treat the entire SRS as potentially compromised until proven otherwise. Proper diagnosis requires SRS-safe tools, OEM-approved test methods, and technician training. Generic scan tools often cannot access Lexus SRS details or clear codes correctly, so use a scan tool with full SRS capability.

Common Misdiagnoses

Technicians often replace the knee airbag module or spiral cable without proving an open in the correct squib circuit. Another common mistake involves checking resistance with a standard ohmmeter on an airbag connector. That can damage components and violates safe test practices. Shops also miss simple causes like a partially latched connector, terminal push-out, or harness damage from prior lower-dash work. Some chase low battery voltage or unrelated body codes and ignore freeze-frame and sub-code data in the SRS ECU. Avoid wasted parts by verifying connector integrity, terminal fit, and harness continuity using OEM-approved SRS test adapters and procedures.

Most Likely Fix

The most frequently confirmed repair directions involve restoring circuit continuity at the driver knee airbag squib connector or the SRS ECU connector. Lexus platforms commonly set this code after lower dash trim work, steering column work, or water intrusion that affects terminals. Expect to find a loose connector lock, corrosion, or a broken wire near the knee airbag housing or along the harness routing. Do not treat the knee airbag module as failed until you verify the wiring and terminals with approved SRS methods. After repair, confirm the fix by clearing SRS DTCs and rechecking for immediate reset during the same key cycle.

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: March 30, 2026