都正确。 但二者的含义不同： 我今天开车接了我妹妹。表示你做过的事。 我今天开车接我妹妹。有可能是还没有做的事，只是一个计划或安排。

3--3 Plus, 了 (non-stessed) has still a third usage: used following verbs (both Vt.and Vi.) or verbal phrases to hasten or try to stop something: 吃早饭了！ Time for breakfast! 走了，走了，不然要迟到了。We've got to hurry to go now, or we'll be late. 好了（Note2），好了（Note2），不要老说这种事情了。 Well, well, do not keep talking about such things.

了2 comes at the end of a sentence or a clause, meaning '(if) something having happed or the situation having changed, as what I said'. Namely, it carries a 'reporting tone'. 我已经读了（1）30本书了（2）. I've read 30 books. 他要是知道了(( 了1 or 了2? Note2 ))肯定会高兴的。He'd be glad when he knows it. 我现在终于知道她那时候为什么不让他去了。I now finally come to know why she had not let him go. NOTE2: Sometimes a 了 at the end of a sentence was alleged by some grammarians to be a mixture of both 了1 and 了2. It remains an open question.I'm not as sure as to assertively give an answer,but I think at this moment that if you analysize the use of 了1 and了2, you'll find that there is actually no overlapped field of usage of both.If a 了 appears between a verb or an adj.and the end of a sentence, it can be either 了1 or 了2 (sometimes the objectives,if there is any, can be let out).

3--1 Your use of 了 there is right. USAGE OF 了 Roughly speaking, 了（non-stressed）includes two (or three) grammatical function words: 了1 and 了2. 了1 follows a verb(usually a transitive ) and means '(if) having done'; or follows an adjective', meaning 'comparing with other things or with itsself in a past or future time': 我这学期读了三十本书。I've read 30 books this school term. 这种新产品获得了普遍好评。This new product has won widespred praise. 这个苹果比那个小了许多。This apple is much smaller than that one. 水位比昨天低了0.2米。The water level is 0.2 meter lower than yesterday. 树叶儿红了。The leaves have turned red/The leaves are turning red【NOTE2】. 他比以前胖了许多。He has/had gathered much flesh than ever. NOTE1: When 了1 is used following an intransitive verb or an adjective ( meaning something happed AGAIN AND AGAIN or a situation appeared AGAIN and AGAIN.And the antecedent Vi. and Adj. is urally monosyllable), it comes only in some repetitive or paralel constructions: 整天吃了睡，睡了吃，这样的生活真没意思。Eat and sleep, sleep and eat: living this way all the time cannot be more boring. 她数了又数，（数了又数），还是只有十五个！ She counted and counted, and yes, the number was still 15! 树叶儿绿了又黄，黄了又绿，一晃几年过去了。她早已做了人妻，又做了人母，而他仍然是孑然一身。The leaves had alternatively been green and yellow, yellow and green.Several years pasted in silence,without being noticed. She became a wife and then a mother,and he was still remaining single.

You're right. But it's not exactly right. You'd better say " 我今天开车去接了我妹妹。” You should add “去”。