P0172Lexus NxYears: 1996 - 2026
System Too Rich (Bank 1)
Reviewed by ASE Certified Technician
What does this mean?
Code P0172 indicates the engine control module has detected that the fuel system on Bank 1 is running too rich — there is too much fuel or too little air in the air-fuel mixture.
Disclaimer: This diagnostic code is part of the standard OBD2 system and can apply to Lexus Nx models manufactured from 1996 to 2026. However, please note that the presence of this specific code depends on your vehicle's exact engine configuration, options, and production year.
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Common Causes
Dirty or contaminated MAF sensor
Clogged or faulty fuel injector
Faulty fuel pressure regulator
Faulty oxygen (O2) sensor
Worn or fouled spark plugs
Faulty Engine Coolant Temperature (ECT) sensor
PCM/ECM software needs update (TSB)
Symptoms to Watch For
- Check Engine Light is illuminated
- Rough or unstable idle
- Black smoke from exhaust (running rich)
- Decreased fuel economy
- Rotten egg smell (sulfur) from exhaust
- Strong fuel odor from vehicle