There is a distinction between Avoidant Attachment style, which is basically a personality built on extreme self-reliance and a conflict avoidant personality. It is unlikely that a co-dependent person is an Avoidant Attachment personality, these people have great difficulty letting others in, and letting others help them. Preoccupied/anxious attachment style - these are the people pleasers. They are always looking to ensure there is no conflict, because one way or another, they grew up in a context where conflict and anger were destructive and dangerous. Either they experienced it first hand or this was the family lore - that anger was bad and needed to be suppressed (likely intergenerational). I used to work with a guy who was classic pre-occupied (narcissistic mother extreme) and he would physically shake if he sensed conflict, even between other people. He'd go out of his way to disrupt any conflict building - joking around, changing the subject, whatever diffused the situation. And he was extremely avoidant too. Trying to be all things to all wo/man and couldn't stand to be the bad guy.
Fixers are more likely on the Avoidant Attachment spectrum - self-reliance and all.