P0172 on Audi: How to Diagnose & Fix
System Too Rich (Bank 1)
1 Audi model · 1 documented issue
P0172 on Audi by model: symptoms, diagnosis and fix
Audi TSB 2046724/5 covers sporadic warm-engine no-start or long cranking after the vehicle sits without fully cooling. A rich-mixture DTC may occur, but often there is no DTC. Audi’s procedure distinguishes fuel in the oil from a short-trip profile, ECM software, high-pressure injector leakage and high-pressure fuel-pump leakage rather than assuming one failed component.
Common Symptoms
- Warm-soak no-start with normal starter operation
- Long cranking followed by rough running for a few seconds
How to Fix
Have the dealer read DTCs and ODIS fuel-in-oil value, verify ECM software and perform Audi’s high- and low-pressure holding tests. If high-pressure behavior is abnormal, borescope the combustion chamber to identify a leaking injector. If low-side pressure builds correctly but drops more than 1.5 bar in the first 15 minutes, Audi says at least one HPFP may be leaking and directs replacement of both pumps plus an oil change. Select no pump or injector until the test identifies the path.
Owner tips & cautions
- TipRecord engine temperature and how long the car sat before the hard start; do not approve pumps or injectors without the pressure-hold results.
Sources for this issue (1)
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 Audi?
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 Audi it is documented across 1 model: S8.
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 Audi?
Repair costs vary widely with the root cause and Audi model; each issue on this page carries its own estimate where one is published.
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.