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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


Long Term Fuel Trim Multiplicative. Max Value, Air/Fuel too Lean.


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 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 fault criteria are not fulfilled during the driving cycle, the OK report will made when the ignition is turned off and before the engine stops. Two other types of OK report can also be made:

Type 1: If a diagnostic trouble code has already been stored for the diagnosis and the same running conditions have occurred (coolant temperature above or below 71°C, engine speed ±375 rpm and load ±10%).

Type 2: If there is no diagnostic trouble code stored for the diagnosis or the same running conditions have not occurred.


Fault handling: (For more information, see .)


- 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 %.


For information, see .