一汽丰田卡罗拉维修维修手册(PO171, 7).pdfVIP

汽车技师帮技术资料 05–136 一汽丰田卡罗拉维修维修手册(PO171, 7) DIAGNOSTICS – SFI SYSTEM (April, 2003) 05DIM–01 DTC P0171 SYSTEM TOO LEAN (BANK 1) DTC P0172 SYSTEM TOO RICH (BANK 1) CIRCUIT DESCRIPTION The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim in- cludes the short–term fuel trim and the long–term fuel trim. The short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at stoichio- metric air–fuel ratio. The signal from the heated oxygen sensor indicates whether the air–fuel ratio is RICH or LEAN compared to the stoichiometric air–fuel ratio. This variance triggers a reduction in the fuel volume if the air–fuel ratio is RICH, and an increase in the fuel volume if it is LEAN. The long–term fuel trim is the overall fuel compensation carried out in long–term to compensate for a continu- al deviation of the short–term fuel trim from the central value, due to individual engine differences, wear over- time and changes in the operating environment. If both the short–term fuel trim and the long–term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL is illuminated. DTC No. DTC Detection Condition Trouble Area Air induction system Injector blockage Mass air flow sensor Engine coolant temperature