Back window washer stopped working but the front still does. Do not see any leakage under the car indicating hose is disconnected or broken (used to happen on my Chevy Venture quite often). What could be the problem?

Same place you fill for the front washer fluid ! Your fronts work but not the rear ? There are to washer pump motors on the washer fluid bottle , one for the front an one for the back . Rubber hose goes all the way to the back . If that hose has failed ,to replace it you basically have to pull out your vehicles interior .
Rear Window Washer Hose Replacement - Pump to Endgate
Removal Procedure

1. Remove the left front seat. Refer to Bucket Seat Replacement in Seats.
2. Remove the rear seat. Refer to Rear Seat Replacement in Seats.
3. Remove the endgate/liftgate door sill plate. Refer to Rear Floor Rear Trim Plate Replacement or Liftgate Door Sill Plate Replacement in Interior Trim.
4. Remove the left front and left rear door sill plates. Refer to Door Sill Plate Replacement in Interior Trim.
5. Remove the left body side trim panel. Refer to Body Side Trim Panel Replacement in Interior Trim.
6. Remove the left hinge pillar trim panel. Refer to Body Hinge Pillar Trim Panel Replacement - Left Side in Interior Trim.
7. Fold over the left side of the carpet to allow access to the body harness. Refer to Front Floor Mat/Carpet Replacement and Rear Floor Panel Carpet Replacement in Interior Trim.

Disconnect the washer hose connection (1) from the body harness (2) at the endgate. Remove the air cleaner assembly. Refer to Air Cleaner Assembly Replacement in Engine Controls.
Disconnect the hose (1) from the rear washer pump. Install a plug to the rear washer pump nozzle to prevent washer fluid loss. Push the hose grommet (2) in through the bulkhead.
Pull the washer hose (1) into the vehicle though the bulkhead. Cut the old washer hose off where it enters the body wiring harness (2). Remove the hose end from the vehicle
Or it could be the pump , they go bad . switch the hoses from one pump to the other an see if you get washer fluid at the back ,if you do the pump is bad ,if not the hose or the spray nozzle is clogged . You probably will need to pull the washer fluid bottle to see both pumps

I don't think so, I've recently repaired the same problem on a Scenic.

As the rear works, the pump is OK.

The front washer nozzle could be blocked, try clearing with a pin.

If no go, look under the bonnet, move the heat proofing and you should find that the washer hose has a fork built in, back and front. Disconnect the front from the fork connector and blow up it, is it clear.

In my case, I had to replace the hose from the reservoir to the forked connector. Which meant taking the wheel off and removing the reservoir from the inside of the wing.

If you get this far, make sure to keep all the small hoses and connectors that are in good order. Also give everything a good clean out while its in bits.

check that hoses have not come off or are being pinched when closing your hood

if living in below freezing temp. make sure using all season fluid, check for clog via sediment also in hose or in the outlet/port itself.

try and fill up the washer bottle with water for test and use it. if you hear the pump work keep using it till you see where fluid is leaking out. my guess is a hose is broken and all the fluid is leaking out

One can get a repair kit that includes a new motor pump and wiring clips, or

one can get the original motor that plugs into the windshield wiper fluid reservoir.

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Windshield wiper reservoir (gives idea of how to change the windshield wiper fluid pump motor) Removal & Installation To Remove:

1. Disconnect and isolate the negative battery cable.
2. Raise and safely support the vehicle.
3. Remove the right front wheel and splash shield.
4. Disconnect the electrical connectors from the pumps and detach the rear washer hose.
5. Place a drain pan under the reservoir if it contains fluid.
6. Disconnect the front washer hose at the wiper unit in the engine compartment. NOTE: The front hose will be removed with the reservoir.
   
7. Let the fluid drain from the reservoir.
8. Remove the mounting screws and the reservoir.

To Install:

1. Install the fluid reservoir with the mounting screws.
2. Connect the front washer hose in the engine compartment.
3. Connect the electrical connectors and rear washer hose.
4. Install the splash shield.
5. Install the right front wheel.
6. Lower the vehicle.

just check on the front differential there is the actuation 4WD valve which is operated by means of vacuum. See whether you do have any vacuum leak,broken vacuum hose,or if the actuator itself does not work.

the pump motor likely is bad. get a used washer fluid reservoir at a pick n pull yourself or at car-part.com. page with * is lowest cost.

Pump and Reservoir, Windshield Washer Removal

1. Disconnect the battery ground cable (14301).
   
2. Raise and support the vehicle.
   
3. Remove the RH wheel (1007).
   
4. Remove the RH front fender splash shield (16103). Refer to Section 01-02 for the removal procedure.
   
5. Remove the windshield washer reservoir top bolt.
   
   
6. Disconnect the windshield washer reservoir fluid level sensor electrical connector.
   
7. Disconnect the rear window washer pump electrical connector from the rear window washer pump.
   
8. Disconnect the windshield washer pump electrical connector from the windshield washer pump (17664).
   
9. Place a suitable drain pan under the windshield washer reservoir (17618) and drain the washer fluid.
   
10. NOTE: The rear window washer hose end is color-coded, matching the connector on the rear window washer pump. Match the colors to ensure proper installation.
    
    Disconnect the washer hoses from the windshield washer pump and the rear window washer pump on the windshield washer reservoir.
    
    
11. Loosen the two windshield washer reservoir side bolts.
    
12. Remove the windshield washer reservoir by sliding it out of the side slots.
    
13. Remove the windshield washer pump.
    
    Installation

To install, reverse the removal procedure. Tighten the lug nuts (1012) to 98-118 Nm (72-87 lb-ft).

well, i don't know if it was much of a solution. I figured out there was only one resevoir for the front and rear washer fluid...located the hose going to the rear and disconnected it from the electric pump attaced to the resevoir. Once the hose was disconnected i activated the pump and the fluid shot out of the pump indicating it was working. So, i figured it must be some kinda blockage in the hose line...so, i pushed air through the line in hopes that it might work to clear it out...well, don't know if that was the trick but when i reconnected the hose it worked!

Generally, the pumps will be located in the fluid resivors. Have some activate the washers while you listen for the sound of the pump. It will make a whirring sound. If the pump motor is running, the next step is to disconnect the hose from the pumps and with compresser air, gently blow through the hose. It is common the the hose or nozzles to clog.
Bill

Rear washer pump is located near bottom of washer reservoir, below the left front wheel house extension and between left inner and outer fenders. Have some operate the rear washer switch while you listen in this area to find out if the the pump is running. The hose from the pump routes up along side the reservoir filler neck, into the engine compartment. Just aft of the reservoir neck an in-line connector joins the hose to the engine compartment hose. The engine compartment hose travels the top left front fender wheel house to the dash panel, passing through a grommet into the passenger compartment. In the passenger compartment, another connector joins the engine compartment hose, and then up through the front driver pillar to the headliner, then above the headliner along the left roof to the rear of the vehicle. It comes out above the lift gate, in the hinge gap, and into the lift gate to the nozzle.

Not likely to be stopped up. First find out if the pump is running, and that there's fluid in the reservoir. Look for fluid running out somewhere near the reservoir. The pump isn't running, or the hose is disconnected around the tank. Look for leaks (when running the pump, and reservoir filled) at the lift gate hinge joint.