What does P0170 mean?

This blog will explain the fault code P0170 and also provides the answers to the following questions. What are the causes of the fault code P0170? How to diagnose the P0170 fault code? Can you drive with the P0170 Fault code present? 

What does P0170 mean?

The P0170 is a fault code in electronic fuel injection systems. When this fault code is present in the fault memory of the engine control unit, the mixture formation in cylinder bank 1 is not within a specified range of -4.5 to 4.5. The engine control unit uses the signal from Lambda sensors to maintain the air-fuel mixture at 0.9 to 1.0.

The engine control unit can adjust the air-fuel mixture in the cylinders by controlling the quality of fuel injected in the cylinders. The air mass is determined by either the air mass sensors or the engine control unit can calculate the air mass with the help of the intake manifold pressure and temperature sensor.

The air-fuel mixture can go beyond the adjustment range of the engine control unit due to unmetered air entering the cylinder or too much fuel being injected into the combustion chamber.

In both cases, the Lambda sensor will either send a lower or higher voltage signal to the engine control unit depending on the level of oxygen present in the exhaust gasses. The mixture formation adaptation range depends on the wide band or narrow band oxygen sensors.

What are the causes of the fault code P0170?

The causes of the fault code are listed below:

  • Leak in the intake air system

The air intake system in a petrol engine consists of an intake manifold, throttle valve, and intercooler with turbochargers. The air going into the cylinders is measured by the air mass sensors and it is controlled by the throttle valve.

If there is a leak in the intake air system downstream of the air mass sensor, unmetered air enters the combustion chamber. This unmetered air is the cause of the lean fuel mixture; the engine control unit cannot compensate for the unmetered air.

Leaks can be due to old intake manifold gaskets, cracks in the intercooler hoses, or worn-out throttle valve O-rings. The lambda in the combustion chamber becomes greater than 1 and the engine control unit will save the fault code P0170 with the fault frame freeze data.

  • Stuck fuel vapor purge valve

The fuel tanks of the latest cars are not allowed to be vented into the atmosphere. There is a fuel tank vapor purge system that stores the vapor in a charcoal canister. The purge control valve is operated by the engine control unit.

When it is opened, the fuel vapor is sucked from the fuel tank and mixed with the intake air downstream of the throttle valve. The engine control unit also reduces the fuel injection quantity when the purge valve is opened.

A stuck purge valve is either continuously open and enriches the air-fuel mixture or it does not open, which creates a lean mix. Both the conditional will lead to P0170 and the purging function is built into the programming of the engine control unit.

The charcoal canister is purged during partial load operation and the duration of actuation of the purge valve depends on the capacity of the fuel tank

  • Faulty fuel injector

A fuel injector is used to inject fuel either in the intake manifold or directly inside the combustion chamber. When it remains continuously open, an excess amount of fuel is injected into the combustion chamber.

The engine control unit monitors the fuel injection quantity but a faulty fuel injector cannot inject the specified amount of fuel. Many car manufacturers use injector coding which compensates for the manufacturing tolerances of the injector nozzle.

The engine control unit will try to adjust the PWM signal according to the fuel injector coding but if the specified limit is exceeded, the engine control unit will activate the check engine light to alert the driver.

  • Faulty air mass sensor

An air mass sensor is used to measure the quantity of air entering the intake manifold. If the sensor is damaged or not working correctly, the engine control unit assumes a default valve and goes into fail-safe mode.

The default value is set at -6.5 or 6.5 in the mixture adaptation so that it will generate the P0170 fault code and turn on the check engine light. After replacing the air mass sensor, the mixture adaptation data must be restored, or the engine control unit will continue to run in a fail-safe mode.

  • Faulty lambda sensor

Lambda sensor or oxygen sensor is very crucial for determining the mixture formation. the engine control unit enables the lambda control after the exhaust gasses reach temperatures higher than 400 degrees Celsius.

Additionally, an oxygen sensor heater is also built into the oxygen sensor so that it reaches the operating range more quickly. A faulty lambda sensor can send a lower voltage signal to the engine control unit.

If the voltage signal is not within the range based on the fuel injection quantity and air mass, then fault code P0170 is stored in the engine control unit.

How to diagnose the P0170 fault code?

The procedure to diagnose the P0170 fault code is given below.

  • Perform an initial quick test or read out the fault memory of the engine control unit.
  • Check the actual values of the mixture formation and determine if the mixture is lean or rich. 
  • If the mixture is rich, check the fuel injection quantity and fuel injector for proper functioning.
  • The purge control valve can be checked by temporarily disconnecting the hose and observing the lambda value.
  • If the mixture is lean, perform a visual inspection of the air intake system.
  • Perform a smoke test to identify leaks in the intake system. Once the leak is identified, unmetered air entering the combustion chamber can be stopped.
  • If the fault is due to a faulty air mass sensor then the default values of the mixture adaptation will be at an extreme limit.
  • Vehicles with a faulty lambda sensor can be diagnosed by swapping out the sensor with a good one or checking the internal resistance. Many diagnosis tools also have a built-in program to check the operation of the lambda sensors.

Can you drive with the P0170 Fault code present? 

Yes, it is possible to drive a car with P0170 present in the engine control unit. The fuel economy and the power output of the car will be significantly reduced and the check engine light will stay active.

In some cases where the cause of the fault code is due to faulty fuel injector then the engine can misfire. The misfiring occurs due to more fuel in the air-fuel mixture; this enriched mixture can damage the catalytic converter.


This blog explained the causes and the procedure to diagnose the P0170 fault code. The correct diagnosis for the P0170 is very important otherwise the same fault can occur even after replacing components like air mass sensor and fuel injectors. Similarly, it is also important to reset the mixture adaption data after performing repair work.