How do you repair the wiper assembly on a 1996 Nissan Altima when only one wiper works?

Your problem is a broken linkage arm, that runs from the wiper motor, to the wper arm. This is located under the cowl. Look down into the grill under the lower edge of the windshield, and you will see the arm. This is NOT something that you should try to fix, yourself. You need a shop to do this repair for you.

Not necesary a bloken arm, could be a loose arm. There is an assembly part betwen two arms and it's a press-assembly so maybe its just a loose part. Let me guess, it's the driver side wiper, right?

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i had that same problem in my 1996 Nissan altima. it happened to the driver side wiper.. what i did was i went under the hood and pulled up that rubber piece over the shield that keeps the leaves, etc, from getting into the car. then i undid the nuts that held the plastic piece down. then i saw that the metal had rusted and the end of the arm was no longer screwed on. i fixed it once with a ziptie but the arm cut through that after 2 weeks. then i went to Home Depot and bought a round metal thing that screws on to pipes to hold them together. i held the arm to a piece of metal above it and then i took a tube of grease (some sort of car grease that costed like 4$ or maybe less) and i squeezed it all in there to stop it from making a horrible scraping sound. it sounded bad for the first few days that i used my wipers but now it sounds fine and it works perfect. its a cheap 6$ fix. it only took about 15 minutes to do it.