If you have power in the garage, you could set up a heating pad designed for pets. Peeing in the house would be a dealbreaker for me.

Dr. Elsey's Cat Attract Litter might work. Or try outside dirt mixed in or on top.

Here is a link some ideas litter box training

more tips

another link

Good Luck!

As some of the links mentioned, avoid scented litter and bring in some of the soil from outside and place it on top of the litter. Also bring in some of his poop.

Where is the litter box located? If he can't see it he's not going to seek it out. Place it in an easily noticeable and accessible location and once he's using it you can slowly move it elsewhere. I would set up 2 boxes......just in case.

My outdoor cats easily switched to Fresh Step Unscented Litter. Also, use an open box, not an enclosed one.

If he has to live in the garage, check out panel heaters (in addition to a heated pad).....they're much safer than the forced air heaters. I've used several brands of heated pads and this is the best one I've found. It comes with a nice fleece cover and I always buy the medium size since I have large cats. Checked around for best price.

I will try these tips. I left him in the house one night with his food bowl, water, litter box and bed in the mud room. He actually used the litter box because he couldn't get out of the room, but the next day he tried to pee on the carpet again and I put him outside. He knows what its for but he doesn't like it. I did buy a lighter, unscented litter. If he doesn't use that I can try soil mixed in. If all else fails, the heating pad sounds like a good idea. Thanks for the suggestions!

glaser, this is what I was thinking, but keep him just in there at night when I go to bed. It will keep him safe and hopefully he will get in the habit. I can't keep getting up in the middle of the night to let him go potty, I have work the next day, so I think this may work out or at least its worth a try.

The fact that he used the litter box while kept in the mud room seems promising. I agree you should mix some dirt in with the litter—you can gradually phase it out once he gets in the habit of using the litter box. Dr. Elsey’s cat attract litter or his ultra precious cat litter (unscented) are good ones to use.

Make sure to clean the carpet using an enzymatic cleaner (Nature’s Miracle makes a cat specific spray version). You want to remove any hint of urine to prevent recurring peeing in that spot.

I am so happy you are giving this guy a chance! I do so hope this works out!

We have been taking care of a feral cat for a few years and although I'd love to bring him inside, he won't even let me pet him so, we build "Jake" his own little cat house on our covered porch, lined with foam, then blankets and I've also gotten 2 Snuggle Safes from Petsmart...It's like a fat frisbee and you heat it in the microwave and this stays warm for up to about 12 hours...I put it between the blankets, one in the morning, the other in the evening and Jake is toasty warm....Just a thought.......