2002 Envoy Forward / Back seat motor no longer functioning

Yes, if you purchase a manual set is will bolt in just the same so long as its the same model and year as they do change from year to year.

You don't mention what year your Yukon is ? This could very well be a control Module problem .
I'll post how the power memory seat's work or are suppose to work !

Memory Seats Description and Operation

Battery voltage is supplied to the memory seat module through a 25 A circuit breaker. The memory seat module supplies the seat adjuster switch assembly with a battery positive reference voltage. While the seat adjuster switches are in an inactive state the switch contacts are closed to the adjuster switch common circuit. When a seat adjuster switch is pressed to an active state the switch contact is closed to the reference voltage circuit. Battery voltage on a switch signal circuit indicates to the memory seat module the switch status is active. Each seat adjuster motor is controlled by the memory seat module through 2 motor control circuits. While the seat adjuster motors are in an inactive state the motor control circuits are closed to ground circuit contacts within the memory seat module. The memory seat module operates the seat adjuster motors by switching one of a motors control circuits to battery voltage. The seat adjuster motors are bidirectional and the direction of adjuster motor rotation is determined by which of the adjuster motor control circuits is switched to battery voltage while the other remains grounded.


Memory Set/Recall Operation
The seat adjuster motors are equipped with internal position sensors. The adjuster motor position sensors are monitored by the memory seat module and are used to determine the seat position when storing or recalling memory settings. The driver seat adjuster motors use potentiometer type position sensors. The position sensors are supplied with a 5 V reference and ground circuits from the memory seat module. The position sensor signal circuits return to an analog input within the memory seat module. During adjuster motor operation the position sensor provides a voltage change proportional to the change in revolution of the adjuster motor shaft. The memory seat module monitors the voltage from the position sensor signal circuits to determine the adjuster motor positions when storing or recalling memory seat position settings.
The memory recall switch assembly on the driver door provides inputs to the driver door lock/window switch. Battery voltage is supplied to the memory recall switch assembly from the driver door lock/window switch. When a RCL 1, RCL 2, or EXIT switch is pressed, the switch contacts close the appropriate switch signal circuit to the battery voltage supply circuit within the memory recall switch assembly. When the driver door lock/window switch receives active switch signals from the memory recall switch assembly, the appropriate commands are sent to the memory seat module using the GMLAN Serial Data circuit. The Body Control Module software version determines the personalization features available.
Memory seat recall operation is allowed only with the transmission selector lever in the PARK position while the ignition is on. The transmission selector lever position data is provided to the memory seat module by a message through the GMLAN Serial Data circuit.

There are somethings listed you are not familiar with , like GMLAN Serial Data circuit ,maybe Body Control Module software etc... GMLAN is a communincation network that the computers on the vehicle uses to share information , transmit commons etc... you can google it to read about it .

There are DTC'S - diagnostic trouble codes that can set in the module in control . Do you know what DTC'S are .

DTC Descriptors
DTC B1825 01: Driver Seat Recline Position Sensor Circuit Short to Battery
DTC B1825 06: Driver Seat Recline Position Sensor Circuit Short to Ground or Open
DTC B1825 5A: Driver Seat Recline Position Sensor Circuit Plausibility Failure
DTC B1850 01: Driver Seat Lumbar Horizontal Position Sensor Circuit Short to Battery
DTC B1850 06: Driver Seat Lumbar Horizontal Position Sensor Circuit Short to Ground or Open
DTC B1850 5A: Driver Seat Lumbar Horizontal Position Sensor Circuit Plausibility Failure
DTC B1860 01: Driver Seat Lumbar Vertical Position Sensor Circuit Short to Battery
DTC B1860 06: Driver Seat Lumbar Vertical Position Sensor Circuit Short to Ground or Open
DTC B1860 5A: Driver Seat Lumbar Vertical Position Sensor Circuit Plausibility Failure
DTC B2355 01: Driver Seat Front Vertical Position Sensor Circuit Short to Battery
DTC B2355 06: Driver Seat Front Vertical Position Sensor Circuit Short to Ground or Open
DTC B2355 5A: Driver Seat Front Vertical Position Sensor Circuit Plausibility Failure
DTC B2365 01: Driver Seat Rear Vertical Position Sensor Circuit Short to Battery
DTC B2365 06: Driver Seat Rear Vertical Position Sensor Circuit Short to Ground or Open
DTC B2365 5A: Driver Seat Rear Vertical Position Sensor Circuit Plausibility Failure
DTC B2375 01: Driver Seat Assembly Horizontal Position Sensor Circuit Short to Battery
DTC B2375 06: Driver Seat Assembly Horizontal Position Sensor Circuit Short to Ground or Open
DTC B2375 5A: Driver Seat Assembly Horizontal Position Sensor Circuit Plausibility Failure

5) Memory Seat Module is under the front of the driver seat , you could look under an see if all the connectors are fully seated.

The best diagnostic step would be to hook up the factory scan tool an see what the computer is seeing as far as inputs from the switch an outputs it's sending . I wouldn't suggest you take the seat apart an try testing electrical inputs etc.... unless you very familiar with automotive electrical systems an circuits .

There are 3 electric motors on the seat. One is forward and back, one is front up and down, and one is rear up and down. The switch changes the polarity back and forth to achieve the proper movement. I think the wire color for the forward and back motor is yellow with a white tracer and red with a white tracer. so if the switch gives the motor positive voltage to the yellow with a white tracer and grounds the red with a white tracer the seat moves forward. If the switch gives the red with a white tracer positive and the yellow with a white tracer ground the seat moves back. (or the other way around). So we can safely say it is in the switch.
Good luck and God Bless

First try as fallow, get in to the seat, then keep tight your foot on floor and give a good press backward to the seat and operate the seat switch towards back, just release and do it again keep going that way it will start to move back words, if it start to move do it few time and do it every time you get in to the car at least two time per day continue it for one week, It will be OK otherwise need chassis no for more information,

Electric or manual??? If electric one of the motors has gone out. If the kids were playing with it they may have held the button down causing the motor to spin while the seat was all the way foward and it will just burn the motor up after so long. Also the switch could be bad. Unfortunatley being that its power there is no way to manually move the seat back without the motor turning or removing the seat and spinning the motor sprocket by hand...

You can move the drivers seat back by turning on the power, getting in the seat and position your feet firmly on the fron flor with your back firmly against he seatback, and then engage the switch pushing back - while pushing like hell with your feet. You can actually hear the seat drive shaft turning while the seat moves back. The principle should be the same for moving forward, but pressure would have to be aplide to the back of the seat.

Before you start beating up thing's , test the electrical circuits. Do you know anything about automotive electrical systems ? How to use a volt meter an a wiring diagram to test for B+ power to the switch an testing the ground .
Does your envoy have memory seats ? Your vehicle has four or more electric motors to control back an foward , up an down etc.. the odds of more then one motor being bad at one time are highly unlikely .
Look under the seat any trash under there keeping it from moving ?
If you have memory seats there is a control module involved in making the seats work . If it has memory seats it could have DTC'S - diagnostic trouble codes .
DTC B1735, B1740, B1745, B1750, B1755, B1760, B1815, or B1820
The seat adjuster switches are inputs to the driver and passenger seat modules. The seat modules supply the adjuster switch assemblies with a battery positive switch supply circuit and monitor the switch signal circuits. In an inactive state the switch signal circuits are floating and when a switch is pressed the signal circuit is closed to the switch power circuit within the adjuster switch assembly. When battery voltage is present on the switch signal circuit the seat module determines the switch status to be active.
DIY Blazer GMC Jimmy Power Seat Control Diagnostics and Repair Electric...

Does it make any noise when you push the switch forward or back? Could be a bad switch and or motor?

If the seat track mechanism has play, it is possible that it is binding up because it reached the rearward limit of its travel, stalling the motor. You can try having someone <carefully> force the seat forward from behind as you engage the "forward" function of the switch. This may be enough to "unbind" the mechanism- if this is the issue.
Otherwise, it is likely that the forward function of the ower seat switch is no longer working. You could try to spray some electrical contact cleaner into the switch (being careful not to stain the seat upholstery), let it dry and then try the switch again, possibly wiggling it as you push it forward. If this works, it is likely a temporary fix and you should replace the switch to prevent it happening again.

Use a hammer and tap each of the travel rails on seat, this worked great for me, something just gets misaligned in there.