Can I get a replacement vehicle if a fault has not been fixed?
The seller has only one opportunity to repair your vehicle if there is a breach of your consumer rights. You can allow the seller a further attempt at repair if you wish. However, if you give them this opportunity, you will not be able to ask for a different remedy until that repair has either failed to rectify the issue, or another problem occurs.
If you are offered a replacement vehicle, it should be like-for-like so far as is possible. However, if you request a newer model or one with lower mileage, or a car with a higher specification, you may be asked to make some payment towards this.