I never had to supply a W-2 for a vehicle loan. Just my SSN. I almost always get unsecured loans too. They just dump money into your bank account and say "please buy a car with this" and you keep the title. For a mortgage you do have to validate your income. The work around is to just buy your house in cash, I guess (sigh). So I guess mortgage loans leave you open there, but those happen less frequently and may not be good map of income level on a shorter period.
Once in a while they want to see a bank statement or two showing actually paycheck deposits, but I only ever saw that on a mortgage. Once for the car loan they asked to see a balance or two via bank statement. So I showed them a bank account sitting around the $$ for the vehicle loan.
I tend to just avoid loans if at all possible now though.