Suppliers makes sense, because there is a whole lot of gray area stuff in this regard. In the US, for example, many parts suppliers started out as subsidiaries or outright branches of car makers, and were spun off. A lot of effort went into creating legal and financial structures that at least limited the amount of favoritism between, say, Delphi and GM, for example. Nevertheless, it often turned out that even the nominally independent parts suppliers still had a large portion of their business with their former parent companies. And car makers actually deal directly with parts manufacturers; they don’t deal directly with consumers.
There are a few reasons I don’t think price fixing is terribly likely or would be very effective at the level of the prices consumers pay for cars. One is that the consumer deals with a dealer, not the manufacturer, at least in the USA, and here the dealers have a lot of legally-protected independence. It’s quite hard for a manufacturer these days to pressure dealers much on anything. Even if Ford and GM got together to fix prices, they’d have to get their dealers to go along. The dealers are independent and often have more than one marque they sell, too, so anything that limited their freedom to negotiate with customers would simply have them threaten to start selling, say, Toyotas or whatnot.
Another is that the product, cars, simply doesn’t lend itself to price fixing in my mind. Even though from one angle you can look at cars as appliances, they’re really not. People pick them for a host of often seemingly irrational reasons, and seemingly minor differences in looks, trim, or “feel” determine whether people buy this one or that one. How would you fix prices, say, between a Focus and a Cruze? They appeal to such different audiences and the entire marketing strategy of the manufacturers is based on exploiting those differences–and using price to balance out areas where their model falls short. Manufacturers are always shifting their options, styling, and packaging of deals to get buyers interested, and price fixing would severely limit that flexibility. Besides, I really don’t think any automaker wants the buying public to say “hmm, they’re all the same price in this segment, so lets get the best rated one,” or something like that. A lot of sales are of cars that may not be as highly regarded as others, but which are cheaper.
And then there is the whole segmented market thing. In effect, there is a high degree of commonality in prices across any given market segment already, because the market sort of pushes things this way. Models that compete directly against each other pretty much already cost the same, roughly speaking. There’s no need to sacrifice flexibility in marketing for some sort of price controls. In short, the consumer market for cars works about as well as it can, given the weird manufacturer–>dealer–>consumer set up.
Finally, margins on new car sales are terrible, A while ago I was reading that the best of the bunch, at the time Toyota, was making maybe two grand per car; GM was like under a thousand.That’s selling to dealers, pretty much. Dealers I’ve read are making maybe 4% profit on the average new car. Fixing prices wouldn’t help, unless you raised them astronomically, and then the bottom would fall out of the market worse than it is doing now. The average cost of a new car in the USA is already somewhere around $35k, and more and more people are leasing to avoid massive payments. Not much more blood to be squeezed from the turnip.