Past tense: David couldn't pay the bill unless he had returned back to the car...

[Nerry]

Let's think that David faced to an incidence yesterday, like I stated below.
Is it possible to say;

"David couldn't pay the bill unless he had returned back to the car and bring his credit card" ?

[Cerberus™]

I'm afraid I don't understand what you meant by "faced to an incidence"; did you mean "had an accident"?

I am not sure I understand the context of your sentence, but this is what it would probably look like:

David couldn't pay the bill unless he returned to the car to get his credit card.

[Nerry]

No, it wasn't about an accident. I'v just wanted to give you an idea of the situation that I explained.

Thanks, I satisfied with your explanation. But, tell me please........

If I put "had returned" instead "Returned" in your explanation sentence, does it change the meaning?

What is the difference between the use of "Had returned" and "returned"?

Please explain..

[Cerberus™]

The sentence you gave is quite complicated, especially without context. In order to get the tenses right, you need to know precisely what you want to express. That's why I can't give you a real answer here.

In a normal sentence, the past perfect "had returned" would mean that the returning took place before the action in the main clause, "couldn't pay", which would be in the past. The past perfect is used to describe a situation that happened before another situation in the past.

In this sentence, "returned" is probably a past subjunctive; the sentence is of the type "if I were rich, I could pay you" => "I couldn't pay you, unless I were rich". If you used "had returned", it would probably be a perfect subjunctive, not a past perfect. But that would make the sentence very complicated, because usually, in a sentence of this type, tenses in main clause and conditional clause should be the same: "couldn't have paid ... had returned ...".