What the OBD-II code p0172 means

Fault code P0172 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P0172 – System Too Rich (Bank 1)
P0172
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P0172: causes, symptoms and repairs

The meaning of fault code P0172

P0172 means that the air-fuel mixture is too rich for the car engine parts to run effectively, containing too much fuel or too little air. The ideal air-fuel ratio, known as the stoichiometric ratio, is about 14.7 If the ratio is too far out of the normal range, it can seriously affect the engine’s performance and the driveability of the vehicle.

Possible causes

  • An excess of fuel due to a leaky fuel injector in a car, faulty pressure regulator, bad absorber valve, or a fuel pump that creates too much pressure.
  • Air flow restrictions caused by a clogged car air filter, vacuum leaks, or problems with the lambda, MAF or throttle position sensor.
  • Faults in the ignition system, such as worn spark plugs, bad ignition coils, broken high voltage wires, or timing errors.
  • Cooling system problems. For example, a thermostat that won’t shut, a defective coolant temperature sensor, or a radiator fan that is constantly running. The uncontrolled circulation of coolant liquid may cause the system to use more fuel in order to heat the power unit.
  • It is also possible that the engine control unit (ECU) is malfunctioning, meaning that the mixture, ignition and exhaust processes aren’t being regulated properly.
Symptoms of the P0172 fault

  • A noticeable increase in fuel consumption
  • A strong fuel or sulphur smell
  • Black smoke coming from the exhaust system
  • A decrease in engine power
  • Misfiring and rough idling
  • Sooty car spark plugs
  • Jerking during acceleration
  • Starting difficulties
Recommended repairs

  • Connect an OBD2 scan tool to the vehicle to read the diagnostic trouble codes that have been registered by the system. Deciphering and linking the DTCs together will help you to identify the root of the problem quickly.
  • Remove contaminants and rust from the electrical components and connector pins using a specialised cleaning agent. The sensors should be removed for inspection and cleaning.
  • Check whether the electronic devices and cables are functioning properly using a multimeter and oscilloscope.
  • Inspect the fuel lines for cracks, deformation and leaks. It is also a good idea to examine the vacuum and PCV hoses. Leaks can be fixed by installing new seals and replacing damaged or worn parts.
  • Check the fuel pressure at the fuel rail with a pressure gauge
  • Damaged, worn or defective parts that cannot be repaired using simple methods, such as a cleaning method, should be replaced. Once you have repaired the system, you can reset the DTCs and erase them from the computer’s archive using the scanner.
Frequently Asked Questions (FAQ)

What does the P0172 code mean?


It indicates that the air-fuel mixture is too rich. This is often a sign of fuel or air leaks, clogging, and technical faults.

Can I still drive my car if this occurs?


This is not recommended. It is better to repair the vehicle as soon as possible to avoid thermal damage caused by combustion outside the cylinders and handling related accidents. Excess fuel can also cause problems such as clogging and carbon build-ups, leading to power issues and overheating. In addition, the resulting black exhaust smoke can be harmful for the environment.

How do I get rid of this error?


Get to the bottom of the error and make sure to fix any damage before trying to reset or remove the codes. Addressing the fault immediately will have the most long-term effect.

Cars the fault code P0172 is most commonly found on

Fault code P0172 - System Too Rich (Bank 1) can occur with any car but is most often found on the following cars:

  • Honda: Accord, Jazz, Civic
  • VW: Polo, Beetle, Golf
  • Mercedes: C180, W203
  • Ford: Focus, Fiesta, Mondeo
  • Peugeot: 208, 308, 207
  • Subaru: Impreza, Outback, wrx

If you get the code P0172 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 0172 appears

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