four wheels and nine doors
It means 4 limbs(?), 9 body openings (7 head, 2 lower) -- so, a human/being in sensual world. By cutting off kama-chanda, one leaves the sensual realm (human would & other sugati realms, is bound to higher heavens). As quick perceived. It seems not related to direct Nibbana (although "with its roots" is mentioned, but the wish was related to the dirty sensual realm).
See also AN 2.35: Samacitta Sutta — Minds in Tune
Further investigations in regard of "cakka", wheel:
More common is Chakra, for the "wheels" and might be also denote old indian models of "life-energy", usualy 5 or 7 charkras, which leads to
The esoteric traditions in Buddhism generally teach four chakras. In some early Buddhist sources, these chakras are identified as: manipura (navel), anahata (heart), vishuddha (throat) and ushnisha kamala (crown). en.m.wikipedia.org/wiki/Chakra
but as still not really proper seeming, a Pali research gives a better answer:
catucakka an instr. of four, a lucky tetrad, a fourwheeler of the body as expressing itself in the four kinds of deportment, iriyāpathas A ii.32; S i.16, 63 (catucakkaŋ). In this sense generalized as a happy state, consisting of "4 blessings": paṭirūpadesa -- vāsa, sappurisûpassaya, atta -- sammāpaṇidhi, pubbe -- kata -- puññatā, https://dsalsrv04.uchicago.edu/cgi-bin/app/pali_query.py?qs=Cakka&searchhws=yes
(sugati loka, human with certain merits)
bog: refers to birth in a womb, phlegm... swamp. The questioner obiviously aware of asubha of body, form.