Trouble Codes

Fault codes P0171 and P0174

Fault codes P0171 and P0174

The codes mentioned in the title point to two different types of faults

  • P0171 – for a poor fuel-air mixture feeding the cylinder block No. 1
  • P0174 – for a poor fuel-air mixture feeding the cylinder block No. 2.

Both codes inform that the mixture feeding cylinder block no. 1 or 2 was too poor, therefore in order to obtain correct operation of the mixture composition regulation system, the petrol injection time was increased, but the value of gasoline injection time increase exceeded the value adopted in the program. For fault code P0171 or P0174 to be registered in the controller’s memory, the condition saved in the program must be satisfied, that is, the LONG FT X and SHRT FT X parameter values ​​must reach or exceed the values ​​saved in the program.

For example, in some GM models, these codes are registered if two conditions are met simultaneously:

  • LONG FT X = 25% – this is the upper limit value of the LONG FT X parameter specified in the program;
  • SHRT FT X ≥12% – working control system, enriching the mixture, caused that the value of the SHRT FT X parameter reached or exceeded its upper limit value, defined in the OBDII / EOBD system program.

Information about the upper limit values ​​of LONG FT X and SHRT FT X parameters, exceeding which the error code P0171 or P0174 in the given car model is stored, should be given in the manufacturer’s service documentation. The values ​​of the parameters LONG FT X and SHRT FT X, which were at the time of recording the fault codes, can be read after selecting the function “Frozen parameters”. Do not delete the fault code before reading the parameter values ​​saved in the “frozen parameters”, as they may be helpful in detecting the cause of the fault.