P0172 on Buick: How to Diagnose & Fix
System Too Rich (Bank 1)
1 Buick model · 1 documented issue · 1 critical · $180-$650 repair
P0172 on Buick by model: symptoms, diagnosis and fix
On Gen1 Envisions the crankcase ventilation (PCV) valve integrated into the cam cover sticks or fails, letting unburned fuel wash past the rings and accumulate in the crankcase. Owners find the oil level rising above the full mark, a strong gasoline smell in the oil, and a rich-running check engine light. GM addressed it with TSB 18-NA-246, which pairs a PCV valve replacement and oil change with an ECM recalibration. Left alone, the diluted oil loses viscosity and accelerates bearing and timing-chain wear.
Common Symptoms
- Engine oil level rises above the full mark between changes
- Strong gasoline odor in the engine oil
- Check engine light on
- Rough idle or reduced fuel economy
- Thin, watery-looking oil on the dipstick
How to Fix
Follow GM TSB 18-NA-246: replace the PCV valve/cam cover assembly, perform an oil and filter change with the correct spec oil, and reprogram the ECM with the updated calibration. Re-check oil level after several hundred miles to confirm the level is no longer climbing. If dilution ran long, inspect the timing chain for stretch before returning the car to service.
Sources for this issue (2)
P0172 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0172 mean on a Buick?
P0172 stands for "System Too Rich (Bank 1)." P0172 means the engine computer has determined the air/fuel mixture on bank 1 is too rich — there is too much fuel relative to air. The PCM watches the oxygen sensors and fuel trims; when it must repeatedly cut back fuel to compensate for an over-rich condition and hits its correction limit, it sets this code. Bank 1 is the side of the engine containing cylinder number one. You may notice poor fuel economy, rough idle, a sulfur/rotten-egg smell, black exhaust smoke, or fouled spark plugs. On Buick it is documented across 1 model: Envision.
What are the most common causes of P0172?
The most common causes of P0172 are: Dirty or faulty mass airflow (MAF) sensor, Leaking or stuck fuel injector, High fuel pressure (faulty regulator), Faulty oxygen sensor giving skewed readings, Clogged or dirty air filter, Leaking evaporative purge valve adding fuel vapor, Engine coolant temperature sensor reading too cold, Worn spark plugs causing inefficient combustion. The specific cause varies by vehicle.
How much does it cost to fix P0172 on a Buick?
Published repair estimates on Buick range from $180 to $650 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0172 on a different make?
View P0172 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.