Fault Conditions

P0172
Long Term Fuel Trim Multiplicative. Min Value, Air/Fuel too Rich.

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 does not restart until next driving cycle.

Enable conditions:
- Engine running and closed loop active. One multiplicative and one additive adaptation have been performed.

Fault criteria:
- Multiplicative adaptation below -25% for more than 30 S.

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

System reaction to a fault:
- None.

OK report:
- Provided that fault criteria have not been fulfilled during the driving cycle, an OK report will be given when the ignition is turned off and before the engine has stopped. 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 temperature over or under 71 °C, engine speed 375 rpm and load 10%). Type 2: If there are no diagnostic trouble codes stored for the diagnosis or the same operating condition have not arisen.

Fault handling: See "Fault diagnosis, general" for more information.
- Type II.

Diagnostic help
The engine's fuel requirement is 25% less 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, since 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, then air leaks between the compressor and the throttle are checked for first and then the mass air flow sensor is changed.

If the air quantity is OK, then the fuel supply is checked, i.e. pressure, response, pump flow and finally the injector functions in the diagnostic tool related to the fault:
- Diagnostic status for the diagnosis.
- 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.

Proceed to Diagnostic Procedures Checking the Manifold Absolute Pressure Sensor