What Does P0172 Mean on Your 2022 Lexus IS?
A P0172 code on your 2022 Lexus IS means the engine control module has detected a rich fuel condition on Bank 1. The 2022 IS lineup includes three distinct engines: the IS 300 RWD with a 2.0L 8AR-FTS turbocharged four-cylinder (241 hp), the IS 300 AWD with a 3.5L 2GR-FKS V6 (260 hp), the IS 350 with the same 3.5L V6 tuned to 311 hp, and the performance IS 500 with a 5.0L 2UR-GSE naturally aspirated V8 (472 hp).
On the 2.0L turbo, Bank 1 is the only bank. On the V6 and V8 models, Bank 1 is the bank containing cylinder 1. The P0172 code specifically flags that bank's fuel mixture as too rich.
Symptoms You Might Notice
- Check engine light on
- Decreased fuel economy
- Rough or uneven idle
- Strong fuel smell from the exhaust
- Black soot on exhaust tips
- Reduced throttle response or power
- Potential misfires under load
Common Causes of P0172 on the 2022 Lexus IS
- Dirty MAF Sensor — The most common culprit across all IS engines. Contamination causes the sensor to under-report airflow, leading to over-fueling.
- Boost Leak (IS 300 RWD) — The 2.0L turbo has intercooler piping that can leak at clamp points or develop cracks from heat cycling.
- Upstream O2 Sensor Failure — A sluggish or drifting oxygen sensor on Bank 1 causes the ECM to miscalculate fuel delivery.
- Leaking Fuel Injector — An injector that doesn't seal properly drips fuel into the cylinder, especially common on higher-mileage V8 engines.
How to Diagnose the Problem
- Read all DTCs — Check for codes on both banks (V6/V8) and any boost-related codes (turbo).
- Analyze fuel trim data — LTFT values below -10% on Bank 1 confirm rich running.
- Test MAF sensor — Compare g/s readings to Toyota specs at idle, 2500 RPM, and wide-open throttle.
- Inspect boost system (IS 300 RWD) — Smoke test the charge piping.
- Monitor O2 sensors — Check Bank 1 Sensor 1 for proper switching frequency and voltage range.
- Perform injector balance test — Identify any injector contributing more fuel than others.
Repair Options and Cost Estimates
Costs vary by engine. The IS 500 V8 commands premium pricing for parts and labor due to its performance nature and more complex layout.
- MAF Sensor Cleaning — DIY: $8-$12. Shop: $80-$150.
- MAF Sensor Replacement — Parts: $115-$250, labor: $80-$150. Total: $195-$400.
- Boost Pipe Repair (IS 300 Turbo) — Parts: $50-$175, labor: $90-$200. Total: $140-$375.
- O2 Sensor Replacement — Parts: $135-$290, labor: $90-$180. Total: $225-$470.
- Fuel Injector Replacement — Parts: $75-$200 each, labor: $200-$450. Total: $275-$650 per injector (V8 higher end).
Can You Fix This Yourself?
MAF cleaning is always a great first step — easy, cheap, and often solves the problem. O2 sensor replacement is a moderate DIY job on most IS models. Boost pipe work on the turbo requires patience but is doable. The V8 IS 500 has limited engine bay space, making most repairs more challenging for DIYers.
Prevention Tips
- Use premium fuel (91+ octane required for all IS models)
- Replace the air filter every 15,000-20,000 miles
- Follow the Lexus maintenance schedule
- Use only OEM or quality dry air filters
- Monitor fuel economy trends as an early warning sign