P0172 – O2 Sensor Bank 1; System Too Rich (VW)
Other than the check engine light, the driver is not likely to notice any other symptoms with this code. Sometimes, P0172 will also be accompanied by P0299 in turbocharged engines, which is a further indication that not enough oxygen is getting into the cylinders during firing.
The most likely culprit for this code in your Volkswagen will be a dirty or clogged air filter. However, other potential causes include:
- A dirty or faulty mass air flow (MAF) sensor
- A vacuum leak
- A fuel pressure problem (too high), or
- An exhaust leak before the first O2 sensor
To begin diagnosis, note the codes tripped and replace the air filter. If the codes clear on their own – or are cleared and do not come back – then your problem is likely solved.
If P0172 or P0175 were the only codes tripped (by themselves, not in concert), you may have an exhaust leak on one side of the engine between the cylinder head and the first O2 sensor.
If more than one code was set, but the second is merely a P0175, then the air filter and/or MAF cleaning may still resolve the problem.
If P0299 or another turbo-related code or oxygen-related code is set as well, however, then there may very likely be a leak in the exhaust or, more likely, a vacuum leak or fuel pressure issue.
Author Jason Lancaster is the editor of AccurateAutoAdvice.com, a website that helps consumers navigate buying, selling, and maintaining their vehicles. Jason also works with VWPartsVortex.com, a website that sells OEM VW parts online at wholesale prices.