What P0131 Means on the 2022 Lexus NX
Code P0131 on your 2022 Lexus NX indicates the Bank 1 Sensor 1 air-fuel ratio sensor is reading below the ECM's expected voltage range. The second-generation NX (AZ20 platform) launched in 2022 with multiple engine options: the 2.5L four-cylinder (A25A-FKS) in the NX 250, the 2.4L turbo four-cylinder (T24A-FTS) in the NX 350, and the 2.5L hybrid (A25A-FXS) in the NX 350h. Since all engines are inline-four configurations, there's only one bank — Bank 1 Sensor 1 is the upstream wideband A/F sensor before the catalytic converter.
Symptoms
- Check engine light on
- Reduced fuel economy below expected range
- Subtle rough idle that disrupts the NX's smooth character
- Minor hesitation during light acceleration
- On the NX 350h, the engine may run more than expected
Causes on the 2022 NX
1. A/F Sensor Failure or Contamination
The Denso wideband A/F sensor in the NX is a precision component. On the NX 350's 2.4L turbo, the sensor sits downstream of the turbocharger where exhaust temperatures are significantly elevated compared to the naturally aspirated models. This extra heat can degrade the sensor's pumping cell faster than expected. On all models, contamination from engine oil vapors through the PCV system or low-quality fuel can poison the sensing elements.
2. Wiring Issues
The NX's compact crossover design packs the engine bay tightly. The A/F sensor harness routes near the turbo (on the NX 350) or exhaust manifold (on other models), where heat can damage insulation. Connector corrosion from moisture or road salt is also possible, particularly where the harness passes through the firewall area.
3. Exhaust Leak
A leak at the exhaust manifold-to-head gasket or at the turbo-to-downpipe connection (NX 350) introduces ambient air into the exhaust stream. This makes the A/F sensor read lean, triggering P0131. On the turbo model, check the downpipe gasket and bolted flanges carefully.
4. Lean Condition
A genuine lean condition from a boost leak (NX 350), vacuum leak, MAF sensor issue, or fuel delivery problem causes the sensor to accurately report lean operation. Check for P0171 as a companion code to confirm.
Diagnostic Steps
- Scan for all codes and check for P0171 companion code.
- Monitor A/F sensor pump current with a capable scan tool — it should respond smoothly to throttle changes.
- Inspect the sensor connector for moisture, corrosion, or heat damage.
- On the NX 350, check the turbo-to-downpipe connection for leaks.
- Review fuel trims — LTFT above +15% suggests a real lean condition.
- If the sensor is confirmed faulty, replace with a genuine Denso unit.
Repair Costs
The 2022 NX should still be under the 4-year/50,000-mile comprehensive warranty and the 8-year/80,000-mile emissions warranty. Out of pocket, a Denso A/F sensor costs $140–$340, and dealer labor runs $100–$220. Total: $240–$560. Turbo-related exhaust leak repairs cost $200–$500.
Act Soon
P0131 is a moderate-priority code. The NX remains drivable, but the luxury crossover's efficiency and smoothness are compromised. If under warranty, there's no cost to you — schedule a dealer visit within a week or two.