P0131 on the All-New 2024 Lexus RX
Your 2024 Lexus RX has triggered code P0131, meaning the Bank 1 Sensor 1 air-fuel ratio sensor is reading below its expected voltage. The fifth-generation RX (AK30 platform) is a completely redesigned vehicle offering the 2.4L turbocharged four-cylinder (T24A-FTS) in the RX 350, the 2.5L hybrid (A25A-FXS) in the RX 350h, and the 2.4L turbo hybrid in the RX 500h. On the inline-four engines (RX 350 and RX 350h), there's only one bank. On the RX 500h with its transverse setup, Bank 1 is determined by cylinder #1 location.
Symptoms
- Check engine light on the dashboard
- Fuel economy below the expected range
- Subtle idle roughness
- Minor hesitation under light throttle
- On hybrid models, the engine may engage more frequently
Likely Causes on the 2024 RX
1. Defective A/F Ratio Sensor
Lexus uses precision wideband air-fuel ratio sensors manufactured by Denso. On a vehicle this new, a factory-defective sensor is the most probable cause. The 2.4L turbo engine in the RX 350 produces high exhaust temperatures downstream of the turbocharger, which can expose sensor weaknesses that wouldn't appear in a naturally aspirated application. The sensor's pumping cell or reference cell may have a manufacturing defect.
2. Wiring or Connector Issue
Assembly-related wiring problems — a connector not fully clicked, a harness routed too close to the turbo, or a pinched wire at a bracket — can cause signal voltage issues. On the RX 350's 2.4T, the tight engine bay means the sensor harness runs close to multiple heat sources.
3. Exhaust Leak
A gasket failure or loose connection between the turbo outlet and the catalytic converter allows ambient air past the sensor. On the new RX platform, the exhaust routing is tightly integrated, and even a small leak at a flanged connection can cause P0131.
4. Software Calibration
As a new platform, the 2024 RX may have ECM software updates that address O2 sensor monitoring thresholds. Lexus periodically releases TSBs for new models to refine sensor calibrations. Your dealer has access to the latest software.
Diagnostic Steps
- This is a warranty vehicle — schedule a dealer appointment for diagnosis.
- If checking yourself, scan live data for the A/F sensor. Wideband sensors show current (milliamps) rather than simple voltage.
- Check the sensor connector for proper seating and condition.
- Ask the dealer about TSBs or software updates for the 2024 RX related to exhaust sensor codes.
- Do not attempt unauthorized repairs that could affect warranty coverage.
Repair Costs
Fully covered under the 2024 RX's 4-year/50,000-mile basic warranty and the 8-year/80,000-mile federal emissions warranty. If paying out of pocket, Lexus A/F sensors cost $150–$350, and dealer labor is $120–$250, totaling $270–$600.
Take It to Lexus
On a 2024 model with full warranty coverage, there's no reason to attempt a DIY repair. Lexus dealers have the factory diagnostic tools (Techstream) and access to TSBs that may resolve P0131 with a simple software update. Schedule your visit and maintain your warranty protection.