Nissan Primera 2000 Windscreen Wiper Interval mode won't work.

You didn't take into account the wiper switch is a input to the BCM - body control module ,or do you know that ? The BCM controls wiper one an wiper two relay's to turn on the wipers .
Wondering if it is the PCB or perhaps a physical problem? Guessing never finds the problem . Reading how they work in factory service repair info should be the first step for someone that doesn't know .
Intermittent Operation
Windshield wiper DELAY operation is a low speed wiper motor function with a variable delay interval between the wiper motor cycles. The DELAY interval is determined by a series of 5 resistors within the wiper/washer switch. During DELAY wiper operation, the signal circuit voltage is further reduced through the DELAY resistors. The body control module (BCM) monitors the voltage on the signal circuit to determine the delay interval between the low speed wiper motor cycles.
If the wiper switch is moved from a longer delay interval to a shorter delay interval, the BCM will command an immediate wipe cycle and reset the delay timer to the shorter delay interval.
Additionally, intermittent wiper operation is vehicle speed sensitive. As vehicle speed is increased or decreased, the wiper interval will also increase or decrease.

Low Speed Operation
When the wiper switch is in the Low position, voltage is supplied through an internal resistor to the signal circuit. The body control module (BCM) monitors the windshield wiper switch signal 1 circuit and energizes the wiper 1 relay which will operate the windshield wiper motor. The wiper motor will operate at low speed, since the wiper 2 relay is de-energized. Low speed can also be commanded with a scan tool by commanding Wiper Relay Cmd. ON and OFF.
High Speed Operation
In the High position, the windshield wiper/washer switch supplies voltage to both the wiper 1 and wiper 2 relay coils. This energizes both relays and allows battery voltage from the wiper 1 relay switched output to the switched input of the wiper 2 relay through its contacts and out the switched output of the wiper 2 relay to the high speed circuit of the windshield wiper motor. The windshield wiper motor will operate at high speed. During HIGH speed wiper motor operation, the wiper switch signal circuit is at the LOW speed signal voltage, and the body control module (BCM) supplies redundant voltage to the wiper relay via the wiper diode.

Wiper/Washer System Components
The Wiper/Washer System consists of the following components:
• Windshield wiper/washer switch
• Body control module (BCM)
• Wiper 1 relay
• Wiper 2 relay
• Wiper diode
• Windshield wiper motor
• Windshield washer pump
• Windshield washer nozzles
• Windshield washer solvent container
• Windshield wiper arm and blade assemblies
• Windshield wiper transmission
• WIPER/SW 10A fuse
• WIPER 25A fuse
Refer to Master Electrical Component List.

DTC B3715 02: Front Wiper Relay Drive Circuit Short to Ground
DTC B3715 05: Front Wiper Relay Drive Circuit Short to Battery or Open

Your best bet , take it to a qualified repair shop.

Wiper arm is loose at pivot. Take caps off at pivot and run motor to rest position. Move wiper arms to rest position and secure nuts.

I’m happy to help further over the phone at https://www.6ya.com/expert/anthony_dda4e0152e94f3c0

bad switch change it.

Wiper blade refills that just snap into place are the best way to service your wiper arms. These vary from standard equipment replacements to high performance tested refills. The cost varies too. From about $5. each to about $20. each...The standard replacements are usually fine...the "stealth" designs are wind tunnel tested, and may perform better for you. I demand a clear windshield, (and all windoes) and I also use "rain-ex" polich on all of the outside glass...Be sure to follow instructions on the rain-ex...It helps all windscreen wipers perform, and last longer. Hope this helps.

is the motor heating ? if it does it has a short

First you must diagnose why windscreen wipers going slow and/or stopping.
In order to find out the cause of wipers stopping you can try follows: 1. Carefully extract the wiper arms from their axles (two pieces). In some cases you need to use an extracting tool. Heed of the windscreen !!! 2. Disassemble the plastic covers from the bottom of the windscreen. 3. With the bonnet up you can start the engine, (transmission in "N" or "P" position and parking brake on). Now you must switch on the control lever of the wipers, and go to the engine compartment. If the wiper motor runs let the wiper motor running for a few minutes and switch off. Go to the step 4. If the wiper motor do not runs you must check first the electrical feeding of the motor. It is necessary to unscrew three bolts of the mechanism and disconnect the electrical coupling (difficult assurance). If the electrical feeding is OK you must replace the motor - steps 5, 6, 7. If not you must check electrical connections, the control switch of wipers and electric cables. 4. Now you must check the two bearings of wiper mechanism with your hand. In the most cases the left bearing is out of order (is very hot). This is the most encounter fault of the wipers running at Audi. 5. For have enough space to manipulation the wiper motor together with their mechanism you must extract the plastic cover of the engine computer box, and extract also the box screws. Then you can move slowly the engine computer box, just for a few milimeters. 6. You must disconnect the electrical coupling of the motor (difficult assurance), unscrew three bolts of the mechanism and extract together with the motor. You must move them slowly between windscreen and engine computer box until the wiper motor go out together with the mechanism. This is the most difficult operation! 7. Now you can repair the bearings, replace entire wiper mechanism or replace the wiper motor. It is not very simply, but it works.
Heed of the windscreen !!!
Refit all in reverse order.

wipers stop halfway up windscreen

The nut holding it on has come loose. You need to tighten it sooner rather than later as the splines will wear out quite quickly. Before tightening it, take the wiper off the windscreen and nip it up. If you leave the wiper on the windscreen, it may not tighten properly.

Sometimes it is neccessary to use a special tool for extract the wiper arm from their axle:
1. Carefully extract the wiper arms from their axles (two pieces). In some cases you need to use an extracting tool. Heed of the windscreen !!! 2. Disassemble the plastic covers from the bottom of the windscreen. 3. It is necessary to unscrew three bolts of the mechanism and disconnect the electrical coupling (difficult assurance). 4. For have enough space to manipulation the wiper motor together with their mechanism you must extract the plastic cover of the engine computer box, and extract also the box screws. Then you can move slowly the engine computer box, just for a few milimeters. 5. You must disconnect the electrical coupling of the motor (difficult assurance), unscrew three bolts of the mechanism and extract together with the motor. You must move them slowly between windscreen and engine computer box until the wiper motor go out together with the mechanism. This is the most difficult operation! 6. Now you can repair the bearings, replace entire wiper mechanism or replace the wiper motor. It is not very simply, but it works. Heed of the windscreen !!! Refit in reverse order. Please Rate my Response! Thanks!

Sounds like the linkage part came off from the motor. You'll have to remove the 2 wipers arms and the plastic tray to inspect further.