Gearhead Garage [cheats] 
God-like mode
Do all the jobs you can. After it says that there are no more jobs, get a cheap car from the auction, fix it up, and try to get more than $20,000, which will get you to God-like mode.

Fast Task Completion
Press INSERT + HOME + PAGEUP on a job and instantly finish it with no hassle!

Fix a car fast
If you want to fix up a car with a bunch of bad parts press Delete + End + Page Down. This will cost you the repair cost. This does not work on heavily damaged (gray) parts.

Easy money
Note: This does not work on high priced or third party cars. Buy an old or new junker from the auction. Do not repair this car. Just take and buy a new car door from the catalog. Put the door or whatever part on the car and auction it. This will generally make anywhere from $78 to $1,000 profit.

Codes

code - effect

big dog - Dragster Wheels
small cat - Small Front Wheels
money - $100,000
engine - Strong Engine