What Does P0172 Mean on Your 2022 Lexus RX?
If your 2022 Lexus RX is throwing a P0172 code, it means the engine control module (ECM) has detected that Bank 1 is running too rich — meaning there's too much fuel relative to the amount of air in the combustion mixture. The 2022 RX 350 is powered by a 3.5L 2GR-FKS V6 producing 295 horsepower. Bank 1 is the side of the engine containing cylinder 1, which on this transverse-mounted V6 is the bank closest to the firewall.
If you have the RX 450h hybrid, the same 3.5L V6 is paired with electric motors, and a rich condition on Bank 1 still points to the same fuel system issues.
Symptoms You Might Notice
- Check engine light illuminated
- Decreased fuel economy (dropping below the usual 20-27 mpg range)
- Rough or slightly uneven idle
- Strong fuel smell from the exhaust
- Black soot buildup on exhaust tips
- Occasional hesitation during acceleration
Common Causes of P0172 on the 2022 Lexus RX
- Dirty or Failing MAF Sensor — The mass airflow sensor can get contaminated with dirt or oil, causing it to under-report airflow. The ECM then delivers too much fuel for the actual air volume. This is the most frequent cause on the 2GR-FKS engine.
- Faulty Oxygen Sensor (Bank 1 Upstream) — The Bank 1 upstream O2 sensor feeds data to the ECM for fuel trim adjustments. A lazy or biased sensor can cause the system to add fuel unnecessarily.
- Leaking Fuel Injector — One or more injectors on Bank 1 may be leaking or stuck partially open, delivering excess fuel even when not commanded.
- Stuck Open EVAP Purge Valve — A purge solenoid that stays open continuously feeds fuel vapors into the intake, enriching the mixture beyond what the ECM expects.
How to Diagnose the Problem
- Scan for all codes — Check for companion codes like P0175 (Bank 2 rich), P0101 (MAF), or EVAP codes.
- Check fuel trim data — Look at long-term fuel trim (LTFT) for Bank 1. Negative values beyond -10% confirm a rich condition.
- Inspect the MAF sensor — Remove and visually inspect for contamination. Compare readings to Toyota/Lexus specifications at idle and 2500 RPM.
- Test O2 sensors — Monitor Bank 1 Sensor 1 voltage and switching rate with live data.
- Perform an injector balance test — Use a scan tool to check for injector contribution imbalance.
- Test the purge valve — Apply vacuum and verify it holds when de-energized and opens when energized.
Repair Options and Cost Estimates
The 2022 RX is a premium vehicle, so parts and labor tend to be at the higher end. Lexus dealer rates typically run $150-$200/hour, though independent shops familiar with Toyota/Lexus are a good alternative.
- MAF Sensor Cleaning — DIY: $8-$12 for cleaner. Shop: $80-$150.
- MAF Sensor Replacement — Parts: $120-$250, labor: $80-$150. Total: $200-$400.
- O2 Sensor Replacement (Bank 1 Sensor 1) — Parts: $150-$300, labor: $100-$200. Total: $250-$500.
- Fuel Injector Replacement — Parts: $80-$180 per injector, labor: $200-$400. Total: $280-$580 per injector.
- EVAP Purge Valve Replacement — Parts: $40-$100, labor: $80-$150. Total: $120-$250.
Can You Fix This Yourself?
Cleaning the MAF sensor is an easy DIY job — it takes about 15 minutes with a screwdriver and MAF cleaner spray. Beyond that, O2 sensor replacement is manageable for experienced DIYers with a jack and O2 sensor socket. Injector work on the 3.5L V6 is more involved due to the intake manifold and is best left to professionals.
Prevention Tips
- Replace the engine air filter every 15,000-20,000 miles
- Use top-tier gasoline (91+ octane recommended for the RX)
- Keep up with scheduled maintenance intervals
- Avoid aftermarket oiled air filters that can contaminate the MAF sensor
- Address check engine lights promptly to avoid secondary damage