Before we go far, I wish to inform you that you can do a degree with a grade C, C-, D+ or D in Kenya but you need to do the following.
To begin with ,remember the grade required for you to pursue a degree in Kenya is at least a C+ ;if you score below C+ in KCSE then you have to start from the lowest level after high school.
If you scored D+ or D plain, you have to enroll for a certificate course, then a diploma course and finally a degree course. A certificate course takes at most 6 months while a diploma course takes at most two years. Once you are through with the two levels, you are eligible to pursue a degree of your choice.
If you scored a C- or C plain, you are allowed to pursue a diploma course, which takes a maximum of 6 months, and later enroll for a degree course.
From what you have seen above, it is possible to pursue a degree in Kenya even if you scored less than C+.