BBC Learning English:Can you fix this sentence?

Wash up your shirt if you have time.

What do you notice about how we use the phrase verb ‘wash up’?
I’m washing up these plates.
I’m washing up this saucepan.
Can you wash up your mug?’
‘Washing something up’ means cleaning the plates, pans, and other things we use for cooking and eating.
But we can also just use wash, too.
I’m washing the saucepan.
When you talk about clothes, we just use the verb ‘wash’.
I need to wash this t-shirt.
We can also say ‘do the washing’ when there isn’t an object. 目的語
I’m doing the washing.
When we add ‘up’, it means we’re washing the plates and dishes.
I’m doing the washing up.
So let’s fix that sentence.

Wash up your shirt if you have time.
Is it ‘wash the car’ , or ‘wash up the car’?
Let us know in the comments.