、。
If the car has trouble, I'll go by bus.
Literal
By-chance car's condition [subject-が] bad-was-[conditional-たら], bus [with-で] go.
調子が悪い ('the condition is bad') is the standard Japanese way to say something — a body part, a vehicle, a machine — isn't running right; the noun 調子 covers physical health, mood, and mechanical state alike. The subject (the speaker) is omitted, as is typical when context makes it clear. 万一 + ~たら + バスで行く is a clean templated 'just in case' contingency.