To read generally on PoF see
https://www.getgcms.com/blog/proof-funds-requirement-express-entry/
As regards your question, IRCC wants that an applicant have sufficient funds to settle in Canada after they become a PR. For this you are required to show funds as per the set threshold. Any liability that you have is usually deducted from that PoF to calculate the funds available to you on the date you file your application.
However, if you are paying the installments on time and they go from a different bank account from the one you are showing for the PoF, you can just not include the car loan. You will not be required to provide a " no liability letter" from the bank. All you need is a letter from your bank for the PoF that you have the funds, the average balance of 6 months and that the funds are unencumbered.