P0171 VW/Audi Fault Code: System Too Lean (Bank 1)
If your CEL (Check Engine Light) is illuminating and you pull a P0171 fault code, it will read out “System Too Lean” or “Fuel Trim System Lean Bank 1”. Now, what does this even mean? Put simply, “System too lean Bank 1” means that the first bank of the engine is receiving too little fuel or too much air. Needless to say, this is not optimal for the engine and should be addressed as soon as possible to avoid further engine damage. The majority of the time when you see this code, it is most likely a vacuum leak, whether it be a vacuum hose or a faulty PCV Valve. Sometimes this would be covered under warranty, but you may be charged for diagnosis if you take it to a dealer. If you’re trying to DIY the fix, see below for written and video DIY guides, replacement parts, and diagnosis tips.
Can I still drive with a P0171 Volkswagen or Audi Fault Code?
This is a very common question when a lot of fault codes pop. Regardless of how bad the vacuum leak is, your engine will not be running smoothly. It is not ideal to drive with this code because the longer it is driven on, the higher likelihood the leak gets bigger causing the engine to run worse and worse over time. So short answer, yes you can, but it is not recommended.
In this guide, we will be providing parts and DIY’s to alleviate this problem on a 2.0t TSI, but if you are looking for parts and DIY’s for another Volkswagen or Audi, let us know in the comments and we will assist you in any way we can!
P0171 VW/Audi Symptoms
- CEL (Check Engine Light) illuminating
- Engine stutter
- Loss in engine performance
- Engine is hard or not turning over
- Engine shutting off and not starting
Causes of P0171 VW/Audi Engine Code
- Vacuum Hose Leaks
- Failing Positive Crankcase Ventilation (PCV) Valve
- Faulty High-Pressure Fuel Pump
- Ignition misfires (Fault Codes: P0300, P0301, P0302, P0303, P0304)
- Intake Air Leak (Fault Code: P0174)
- Faulty O2 Sensor
- Faulty Mass Air Flow (MAF) Sensor
How to Repair a Vehicle with a P0171 Engine Code
If the vehicle is not covered under warranty, we highly advise DIY because the diagnosis is not too difficult. You would want to start at the top of the causes list above and work your way down examining each engine component. The causes are listed from most likely to cause a P0171 code to least likely. Here is a great resource on how to diagnose this fault code.
How to Check for a Vacuum Hose Leak
We’d say about 80% of the time, a vacuum hose leak or a failing PCV valve is the reason your VW or Audi is popping a P0171 engine code. It may be difficult diagnosing a vacuum hose leak, but there is a hose that goes from the vacuum pipe to the vacuum pump that is the main hose to look out for.
How to Replace a PCV Valve
As stated above, a failing PCV valve is another major reason why a vehicle throws this code. In short, a PCV valve catches oil fumes and unburned fuel to reduce emissions. You would be looking at a cost of about ~$400 if you took it to the shop to replace it.
How to Replace an HPFP (High-Pressure Fuel Pump)
Once you start getting into older vehicles, you can start to see the following be reasons. An HPFP does as it sounds; it transforms regular fuel into high pressurized fuel that is needed for direct injection. The cost that would be charged at a shop to replace this is ~$800 mainly due to part costs.
How to Replace Ignition Coils
It is common to have a P0171 code followed by engine misfire codes (P0300, P0301, P0302, P0303, P0304), but it is important to replace or diagnose the three others above before assuming it is a bad coil causing this code. Ignition coils use the battery’s voltage and transform it into the voltage needed for the spark plugs to create combustion. Once you have determined that you have a faulty ignition coil/coil pack, it is suggested to replace all to avoid any future misfires.
Replacement Coil Packs: https://amzn.to/3f64C4m
DIY Difficulty: Easy
DIY Replacement Guide: https://www.custompcguide.net/how-to-change-coilpacks-volkswagen-tsi-eos-mk6-gti-cc-passat-fix-cylinder-misfired/
How to Check for an Intake Manifold Leak
An intake manifold can fail in two ways: coolant leaking and or air leaking into the manifold from outside passageways, which could cause lean scenarios. An intake manifold separates air coming into the engine and pushes it proportionately to the cylinders.
How to Replace O2 Sensor
Lastly, if all the above do not alleviate the problem, it is a slight chance, but a faulty O2 sensor could be the reason for the fault code. An O2 sensor measures the amount of oxygen in the gasses released by the vehicle’s exhaust.
To wrap this up, if your vehicle is receiving a P0171 code, it is more than likely going to be a vacuum leak of some sort. It can be driven for a short amount of time, but it isn’t recommended. As stated above, we wrote this post for a Volkswagen/Audi 2.0t engine, but if you are looking to alleviate this problem for another engine or vehicle, please let us know what you need help with in the comments and we’ll do our best to assist you! We hope this post has helps you and your vehicle!