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.

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 has been performed.

Fault criteria:

-	Multiplicative adaptation exceeding 25% for more than 30 s.

Dependents:

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

System reaction to a fault:

-

None.

OK report:

-

Provided that the fault criteria have not been fulfilled during the driving cycle, an OK report will be generated when the ignition is turned off and before the engine stops. Two types of OK report can be given: Type 1: If a diagnostic trouble code is already stored for the diagnosis and the same operating conditions have arisen (engine coolant above or below 71°C, engine speed ±375 rpm and load ±10%). Type 2: If a diagnostic trouble code is not already stored for the diagnosis or the same operating conditions have not arisen.

Fault handling: (See “Fault diagnosis, general” for more information.)

-

Type II.

Diagnostic help

The engine's fuel requirement is 25% greater under partial load than that which the control module has calculated using 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 quantity is OK, then the fuel supply is checked, i.e. pressure, response, pump flow and finally the injectors.

Functions in the diagnostic tool related to the fault:

•	Diagnostic status for the diagnosis.

•	O2S 1, unit V

•	Multiplicative Adaptation, unit %

•	Closed loop, unit %.

•	Purge Adaptation, unit %.

•	Air mass deviation from calculated, unit %.

See also the description of readings in ”Fault diagnosis, general” for more information.