What the OBD-II code p0171 means

Fault code P0171 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P0171 – System Too Lean (Bank 1)
P0171
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P0171: causes, symptoms and repairs

The meaning of fault code P0171

The DTC indicates that the oxygen sensor on the first cylinder bank has detected lean engine conditions. This means that there is too much air or not enough fuel in the system. The ECU adjusts the air-fuel mixture based on the sensor readings to achieve the optimum ratio (14.7). If it is unable to maintain the correct ratio by injecting more fuel, the computer will register this code. P0171 is often accompanied by P0174 (System Too Lean Bank 2).

Common causes

Symptoms of the P0171 code

  • A loss of engine power
  • Starting problems
  • An increase in emissions
  • Lower fuel efficiency
  • Engine overheating
  • Rough idling
  • Stalling or difficulty accelerating
  • A popping sound in the car exhaust pipe
  • The “Check Engine” light is illuminated on the dashboard
Recommended repairs

Before tackling repairs, the very first thing you will need to do is a diagnostic scan. You can scan the computer using an OBD2 scanner and check the related trouble codes. This will not only help you to identify the root cause of the fault, but could also reveal other hidden problems.

Depending on what you find, the following components may need to be inspected:

  • The vacuum hoses. These include the vacuum lines, air intake pipe, fuel pressure regulator hose, and so on. You should look for any signs of wear, damage or leaks. Leaks can usually be detected using a smoke generator, although not everyone has access to this equipment.
  • The exhaust pipe. The pipe and exhaust manifold gasket should be inspected for leaks as this will directly affect the oxygen readings.
  • Sensor wires and connectors. First, a visual inspection can be carried out to determine whether the wires have burnt out, parts have corroded, connections are loose or the pins are bent. You may also need to check the device’s electrical resistance and voltage using a multimeter. In some cases, a bad connection can be repaired by simply removing traces of corrosion and contaminants from the connectors.
  • The MAF sensor. This component sometimes needs to be cleaned as dirt, oil, dust and other substances can affect its resistivity. Specialised cleaning agents, such as those made with methanol, can remove contaminants including carbon deposits without damaging the parts. You can find detailed guides on how to test MAF devices online.
  • The fuel injection system. Components such as the pump, pressure regulator, and injector nozzles may need to be checked with a multimeter or manometer. A clogged fuel filter may also be the cause of low fuel pressure.

Once you have obtained a proper diagnosis, you can repair the units by cleaning, tightening, and replacing the faulty components. Don’t forget to check the gaskets too as they may need to be replaced to fix or prevent leaks.

Frequently Asked Questions (FAQ)

What does code P0171 mean?


It indicates that there is too much air in the fuel mixture, causing the engine to operate inefficiently.

What causes the P0171 fault?


It is often caused by problems with the components in the fuel injection and exhaust systems. The mixture process is easily affected when there are leaks, components are clogged, and power supply components are unreliable.

Can I still drive my car if this occurs?


This is strongly advised against as a lean fuel mixture can wreak havoc on the engine, causing thermal damage to gaskets and valves. Consulting a professional and getting the car fixed as soon as possible is the best way to avoid further damage and expensive repairs.

How do I clear the error?


It can be cleared properly after the problem has been rectified. All you need to do is connect the OBD2 scan tool to the car via the data link connector and erase the fault codes from the computer’s memory archive.

Cars the fault code P0171 is most commonly found on

Fault code P0171 - System Too Lean (Bank 1) can occur with any car but is most often found on the following cars:

  • Opel: Astra, Corsa, Insignia
  • Toyota: Corolla, Prius, Yaris
  • Honda: Civic, Jazz, Accord
  • Audi: A3, A4, TT
  • BMW: E39, E46, X5
  • VW: Polo, Golf, Beetle

If you get the code P0171 on your car, make sure that the diagnostics are carried out correctly and the error is still relevant. Check for symptoms associated with the problem and explore options for resolving it.

What to do if the fault code p 0171 appears

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