故障现象
一辆2007款卡罗拉轿车,配备自动变速器。车主反映车辆行驶无力,加速没多大反应,车速只能上升到30km/h左右。
故障诊断与排除
试车发现故障现象属实,停车后发现发动机怠速转速高达900r/min左右,明显高于正常数值。
首先分析车辆加速不良。从原理上讲,加速时发动机电脑采集加速踏板位置传感器信号和节气门位置传感器信号,控制节气门执行电机,使节气门打开较大角度,提供大的进气量,在汽缸内形成的可燃混合汽量也大,点燃时产生的能量也大,活塞的做功频率也加大,曲轴的转速加快,从飞轮端输出的扭矩加大,变速器再根据转速传感器等信息,将大转矩最终传递至车轮,车辆提速。
该车加速不良会不会是加速踏板位置传感器或节气门位置传感器出了问题,发动机控制电脑ECM接收到了错误的信息或没接到信息,不执行接下来的控制了呢?还是发动机进入失效保护模式了呢?
失效保护模式即为当ECM内部存储了某些故障码后,ECM便进入失效保护模式,ECM再根据其他信号控制喷油和点火,调整发动机的输出,以确保车辆维持最低车速行驶。分析至此,感觉此车目前状况就是进入了失效保护模式,如果是传感器损坏会有相关的故障码被存储,用KT600调取故障码,故障码有P2102节气门执行器控制电动机电路低电位、P2111节气门执行器控制系统卡在打开位置、P2112节气门执行器控制系统卡在关闭位置、P2118节气门执行器控制电动机电流范围/性能,且都清除不掉。
故障码显示的是节气门执行器的故障代码,检查节气门体总成。首先拔下节气门体插头,检查节气门体5号端子是否有5V电压,用万用表测得电压为5V。插上插头,用引线测量节气门位置传感器信号线6号端子电压,同时踩踏加速踏板,发现6号端子的电压并没随之增大仍保持在0.8V,而且意外发现节气门保持在一个位置并没有动。
再用电流挡分别测量节气门执行器两端子,没有电流。难道是节气门执行器损坏了,使节气门保持在一个很小很小开度的位置,造成了节气门位置传感器信号线电压恒定在一个值?
还是节气门执行器到ECM间的导线断路了呢?拔开节气门体插头和ECM-B31插头,根据电路图用万用表测量B25-2号端子与B31-42号端子间的电阻,为0.53Ω,说明这段导线是正常的没有断路。
用万用表测量B25-1号端子与B31-41号端子间的电阻,为0.52Ω,说明这段导线也是正常的。会不会是节气门执行器损坏了呢?
因为节气门执行器集成在节气门体内,只能更换节气门体总成试试,可谁知,换上好的节气门体后故障还是依旧,难道是ECM内部某些元件损坏了?
更换ECM后故障依旧存在。这时突然想到某些元件之间是有连带关系的,共用电源线或搭铁线,但从电路图上看不出来还有其他元件与节气门体总成有关联。查维修手册,如图1所示,节气门执行器有独立的供电线,即电源从蓄电池出来,经过ETCS保险丝,再经ECM
的+BM端子,传给节气门执行器。+BM不供电,节气门执行器就不会工作。
测量ETCS保险丝是否烧损。打开集成继电器盒盖,找到ETCS保险丝,如图2所示,测量电阻为无穷大,拔下一看,保险丝确实烧损了,更换新的保险丝,故障彻底排除。
故障小结
该故障属于元件损坏后,发动机进入失效保护模式,表现为上述症状。现在电控车基本都有失效保护功能,关键是怎样摸清真正导致进入保护模式的元凶是谁,对症下药,当今的故障诊断,电控程度比较复杂,并不是头痛医头脚痛医脚了,要真正的从现象分析到本质,但这个过程也是不容易的,一个人并不能对所有的车辆都那么熟悉,资料那么齐全,像本例故障就是这样,从电路图上看不出ECTS保险丝还控制着节气门执行器,只有找到更具体的内部电路才豁然开朗,所以只有不断积累、不断总结,我们的技能才会越来越成熟。
原创文章,作者:cesifu,如若转载,请注明出处:http://www.cesifu.com/article/34444.html
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