What Does P0172 Mean on Your 2022 Lexus NX?
A P0172 code on your 2022 Lexus NX indicates the ECM has detected a rich fuel condition on Bank 1. The 2022 NX was a brand-new redesign with multiple powertrain options: the NX 250 with a 2.5L A25A-FKS naturally aspirated four-cylinder (203 hp), the NX 350 with a 2.4L T24A turbocharged four-cylinder (275 hp), and the NX 350h and NX 450h+ hybrids with 2.5L four-cylinder engines paired with electric motors.
Since all 2022 NX engines are inline-4 configurations, Bank 1 is the only bank — meaning the entire engine is running rich when this code appears.
Symptoms You Might Notice
- Check engine light on
- Decreased fuel economy
- Rough or uneven idle
- Fuel smell from the exhaust
- Black soot on exhaust tips
- Sluggish throttle response (especially on the NX 350 turbo)
Common Causes of P0172 on the 2022 Lexus NX
- Dirty MAF Sensor — The mass airflow sensor is the most common culprit. Contamination from dust, oil residue, or aftermarket air filter oil causes inaccurate airflow readings, prompting over-fueling.
- Boost System Leak (NX 350) — On the turbocharged NX 350, intercooler piping or charge pipe connections can develop leaks, causing metered air to escape before reaching the engine.
- EVAP Purge Valve Malfunction — A stuck-open purge solenoid feeds continuous fuel vapors into the intake, creating an uncontrolled rich condition.
- Upstream O2 Sensor Issue — A lazy or biased oxygen sensor sends incorrect data to the ECM, causing improper fuel trim adjustments.
How to Diagnose the Problem
- Scan for all codes — Look for companion codes related to boost, MAF, or EVAP systems.
- Review fuel trim data — Negative LTFT values beyond -10% confirm rich running.
- Test the MAF sensor — Compare g/s readings against Toyota specifications at idle and 2500 RPM.
- Smoke test turbo piping (NX 350) — Identify any boost leaks in the charge air system.
- Test purge valve — Use scan tool bidirectional control to verify proper operation.
- Monitor O2 sensor — Check switching rate and voltage range for Bank 1 Sensor 1.
Repair Options and Cost Estimates
The 2022 NX may still be under Lexus' 4-year/50,000-mile basic warranty depending on mileage. The powertrain warranty extends to 6 years/70,000 miles.
- MAF Sensor Cleaning — DIY: $8-$12. Shop: $80-$150.
- MAF Sensor Replacement — Parts: $120-$250, labor: $80-$150. Total: $200-$400.
- Boost Pipe Repair (NX 350) — Parts: $55-$190, labor: $100-$220. Total: $155-$410.
- EVAP Purge Valve Replacement — Parts: $40-$95, labor: $75-$140. Total: $115-$235.
- O2 Sensor Replacement — Parts: $140-$280, labor: $90-$175. Total: $230-$455.
Can You Fix This Yourself?
MAF sensor cleaning is easy and takes about 10-15 minutes with basic tools and a can of MAF cleaner. For the turbo NX 350, boost pipe inspection is manageable if you can access the engine bay, though a smoke test requires equipment. O2 sensor replacement is a moderate DIY job. Leave injector or deeper engine work to professionals.
Prevention Tips
- Use only OEM or quality dry air filters
- Replace the air filter every 15,000-20,000 miles
- Use top-tier gasoline (87+ octane, premium for NX 350)
- Follow the Lexus maintenance schedule
- Address warning lights promptly to prevent secondary damage