P0171

Read the instructions below then start the fault diagnostic procedure.

Symptom: CHECK ENGINE. Engine may stop straight after starting, run unevenly and misfire.

P0171

Fault symptoms

•	CHECK ENGINE.

•	Engine may stop straight after starting, run unevenly and misfire.

Important

Check the crankcase ventilation for leaks before performing any other fault diagnosis.

See Inspection of crankcase ventilation hoses

DTCs P0101, P0106, P0300, P0455 and P1300 can be generated as a result of the DTCs above when the cause of the DTC is a leak in the crankcase ventilation. Once the leak has been rectified, the other DTC can be deleted.

On-Board Diagnostics

Type of diagnosis:

-	Continuous. But interrupted when fault criteria fulfilled and will not restart until next driving cycle.

Enable criteria:

-	Engine running and closed loop active. One multiplicative and one additive adaptation performed.

Fault criteria:

-	Multiplicative adaptation exceeds 25%.

Dependents:

-	P0116, P0117, P0118, P0131, P0132, P0134, P0444, P0445 and P1105.

System reaction to a fault:

-

None.

OK report:

-

Provided the fault criteria are not fulfilled during the driving cycle the OK report occurs at ignition off before the engine stalls. Two types of OK reports can be given: Type 1: If a DTC is already stored for the diagnosis and similar operating conditions have occurred (coolant temperature above or below 71°C, engine speed ±375 rpm and load ±10%). Type 2: If there is no DTC stored for the diagnosis or similar operating conditions have not occurred

Fault handling: (See section Fault handling II, emission-relayed misfiring or fault in fuel system for more information.)

-

Type II.

Diagnostic help

Under partial load the engine's fuel requirement is 25 % higher than that calculated by the control module on the basis of information from the mass air flow sensor.

Fault diagnosis first determines if the pressure sensors indicate about the same value with the ignition ON, as the mass air flow sensor is then compared with the intake air pressure. If the pressure sensors are OK but the mass air flow sensor value is not correct, the mass air flow sensor must be changed. Air leaks will not generate this trouble code.

If the air mass is OK, then the fuel supply must be checked, i.e. pressure, pressure response, pump flow and then the injectors.

Functions in the diagnostic tool related to the fault:

•	Diagnostic status for the diagnosis.

•	O2S 1, unit V

•	Multiplicative adaptation, unit %

•	Short term fuel trim, unit %.

•	Purge adaptation, unit %.

•	Airmass deviation from calculated, in %.

See also description of read value under "Read Values" menu for more information.