P0172: System Too Rich Bank 1
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Driveable, but a rich engine washes oil off cylinder walls and clogs the converter - do not ignore for months.
Symptoms
- Black smoke or fuel smell from exhaust
- Sooty spark plugs, poor fuel economy
- Rough idle when warm
Likely causes, most common first
- Leaking fuel injector or excessive fuel pressure
- Dirty MAF over-reporting airflow
- Stuck-closed purge valve flooding vapors
- Dead coolant temp sensor faking a cold engine
Read P0172 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0172 means bank 1 runs rich: the computer keeps removing fuel and still sees excess. Too much fuel is entering, or the computer believes more air is flowing than actually is.
Rich codes deserve prompt attention because unburned fuel destroys catalytic converters - often a four-figure consequence of a two-figure sensor. Fuel trim analysis plus a look at live coolant temperature and MAF grams-per-second at idle identifies most causes without parts roulette.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0172
“vehicle may experience driveability issues, which may result in DTCs P0300 (random misfire detected), P0301 (No. 1 cylinder misfire detected), P0302 (No. 2 cylinder misfire detected), P0303 (No. 3 cylinder misfire detected), P0304 (No. 4 cylinder misfire detected), or P0172 (fuel system too rich) or a whirling noise coming from the engine compartment. POSSIBLE CAUSE Based on certain driving patterns and environmental factors, the DTC's stated above may be set or a whirling noise may occur. Apparently only certain vin numbers were affected, mine is not in the list but im still having the exact same issues.”2017 Honda CR-V · Aug 2026
“Have replaced the fuel injectors twice after completing the recalled fuel pump and now getting P0172 code with another bad injector!!! This is a piece of shit and I'm going to trade it in on a Toyota.”2018 Honda CR-V · Jul 2026
“Back to back error codes P0300 P0108 P1404 P0172 Rough running engine. Very strong smell of fuel at two different times while driving. Vehicle not responding to gas pedal while driving on highway. Repairs at thousands of dollars.”2018 Dodge Durango · Jun 2026
Show 7 more owner reports
“I am reporting a failed remedy for Recall 24-009 (23V-858). Following the fuel pump recall, my 2018 Accord stalled in traffic on March 21. On March 24 upon starting my vehicle all warning lights were illuminated on the dashboard, Millennium Honda admitted the O-ring was misinstalled. This error triggered codes P0172/P0176 less than twenty-four hours later. The dealer is forcing me to pay $425 for damage caused by their botched recall repair.”2018 Honda Accord · Mar 2026
“All the warning lights randomly turned on while driving. I took it an independent mechanic and a Honda certified dealership, and both produced the same diagnosis, a replacement of fuel injectors. P0172 and P0301, P0302 The symptoms, noises, lights are all consistent with TSB19-037, which applies to 2017 and 2018 Honda CRVs. From online forums that have experience the issues around 60-80K miles, my CRV having 72K miles is consistent with the failed fuel injectors.”2019 Honda CR-V · Jan 2026
“This is after the recall on 2018-19 Fit Carbon Buildup with Misfire DTCs under codes P0300-P0304) and after fuel injectors are replaced. Current problem is with combination of carbon deposits on intake valves. Failing fuel injector/s causing an incorrect air/fuel ratio with code under P0172.”2018 Honda Fit · Sep 2025
“Failed emissions with code P0172 (System too rich) at 69,000 miles. Warning lights then appeared on the dash for almost every vehicle system, including Brake System Problem, Brake Hold System Problem, Adaptive Cruise Control Problem, Power Steering System Problem, TMPS Problem, Stability Control Problem, and others. Upon inspection, the problem was determined to be with the fuel injectors which needed to be replaced.”2018 Honda CR-V · Aug 2025
“At around 88,400 miles my Enging light came on saying I had an "Emissions Problem." Shortly after the Emissions problem was being signaled, several other lights came on including, ABS problem, Adaptive Cruise Control Problem, Electronic Break problem and several others. I took my car to a Honda dealership's service shop to have a dianostics test run. According the the report the "check found code P0172 fuel systtem too rich." "Performed A/F test, CYL,1,2,3 Failed too rich." And they recommended replacing the injectors and I opted to have it done by them. When asked if that seemed ealrier for fuel injectors to go, the service rep said yes that they typically last the life of the egine.”2018 Honda CR-V · Aug 2025
“All lights on dash coming on. Codes p0172 and p0303 pop up on obd scanner. Mafs , spark plugs, ignition coils and air filters all replaced. Car goes into limp mode. 124,800 miles. Dealer says fuel injectors failed and needs replacing, research shows this is a common issue for the. 2017 crv Honda edition. Mpg never dropped , remained. 33.1. When codes cleared, car functions like normal.”2017 Honda CR-V · Aug 2025
“2017 Honda CR-V with 132118 miles has intermittently been experiencing all dash display alarms activating at the same time for past 25k miles. (ie) hill start assist, brake system problem, power steering system problem, vehicle stability assist problem, etc... This also disabled the lane keep assist and cruise control features on the car. Dealership ran diagnostic and found code P0172 indicating fuel system too rich and confirmed with a failed air/fuel ratio test. This indicated the car needs complete fuel injector replacement.”2017 Honda CR-V · May 2025
Cars that report P0172 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0172?
Driveable, but a rich engine washes oil off cylinder walls and clogs the converter - do not ignore for months.
How much does it cost to fix P0172?
Typical US repair costs range from $20 for the simplest fix (maf cleaning) to $900 in the worst case. The right number depends on which cause your car has - see the causes list.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.