Maybe it was your dog. Maybe it was your baby. Whichever it was, now you have urine stains on your car's upholstery and maybe even the odour of the urine as well. If you get to work on it quickly and use the right kind of cleaner, you stand a chance of removing the stain and the odour so no one will be able to tell that the accident ever happened.
Soak up any remaining urine with a clean paper towel or a rag. Blot it up rather than rubbing so you don't damage the upholstery or drive the stain deeper.
Make a lukewarm mix of soapy water, using 5 g (1/2 tsp) soap and 1.1 litres (1 qt.) warm water. Use a soap with a neutral pH of 7. Sponge the urine stain with the lukewarm, soapy water. If your car has leather upholstery, don't apply a lot of water to it.
Rinse off the suds with cold water.
Mix five parts of water to one part of ammonia in a bucket. Ammonia will act to neutralise the acid in the urine. It will also help minimise any lingering odour. Use a clean sponge or cloth to apply this ammonia mixture to the urine stain.
Let the ammonia mixture sit on the urine stain for at least one minute. Rinse it away with a very wet sponge or cloth.
If the odour remains after you've applied the ammonia mixture, mix 4 g (1 tsp) of baking soda into 240 ml (1 cup) of lukewarm water. Sponge the baking soda mixture onto the area of the stain and let it sit for at least one minute.
Wipe up the baking soda residue with a clean, wet sponge. Check the odour, and apply more baking soda mixture if needed.
Wipe up the entire area with a sponge dipped in lukewarm water.
Blot away the baking soda mixture, if you used it, or the ammonia mixture if that's all you needed. Use a blow dryer to dry the spot and see if the stain has disappeared.
If the urine stain remains, try a commercial stain and odour remover such as Oxy-Clean's Simple Solution, Nature's Miracle or Planet Urine. Many of these stain removers contain enzymes or bacteria that consume the urine molecules. Test the stain remover on a small corner of the upholstery somewhere out of sight before treating the urine stain, to make sure it won't stain or harm the upholstery. Follow the packaging directions when using these products. Repeat this step if needed.
Re-clean your upholstery with warm water and suds after using the commercial stain or odour remover to make sure no harmful chemicals remain.
If you still haven't removed the urine stain and odour from your upholstery, have your car seats professionally steam cleaned. Steam cleaning will reach past the surface of the upholstery into the foam that provides the car seat's padding. If the urine has soaked past the upholstery, getting stain and odour out of the foam might be important to remedy the problem.
Don't use lemon-scented ammonia, because the product contains a dye that can also stain your upholstery.