Wiper only works in wash mode

https://www.youtube.com/watch?v=5a5_JreHnsQ

Make sure you have a good ground

Sounds like a wiring problem:
1. One of the wires attached to a pin in the connector attached to the wiring at the motor (not on the motor) may be corroded or have come loose, making intermittent contact, or
2. One of the wires in the harness between the motor and the switch is crimped somewhere around the tailgate and is intermittently opening, or
3. A bad motor ground wire connection at the tailgate.

Do you know how to test automotive electrical circuit's using a DVOM - digital volt ohmmeter ? Do you know what a wiring diagram is an how to read one ? Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info. year , make , model an engine size. Under system click on body & accessories ,then under subsystem click on wiper/ washer's . Click the search button then the blue link.

Windshield Wiper/Washer System Components
The windshield wiper/washer system consists of the following components:
• Windshield wiper/washer switch
• Windshield wiper motor
• Windshield washer pump
• Windshield washer relay
• Outside moisture sensor
• FRT WIPER 25A fuse
• W/S WASH 15A fuse
Windshield Wiper/Washer System Operation
Accessory voltage and ground is supplied to the windshield wiper motor and provides the power for operating the wiper motor and logic power to the wiper motor module. The WASH, MIST, LOW, and DELAY modes are controlled by the windshield wiper/washer switch through a series of internal resistors. The windshield wiper switch supply voltage circuit is a 12-volt reference from the wiper motor module to the wiper/washer switch, and the switch position determines the point on the resistor assembly where the reference voltage is applied. The windshield wiper switch signal 1 circuit supplies the voltage from the resistor assembly to the wiper motor module and the signal voltage determines the operating mode. High speed operation is controlled by the windshield wiper/washer switch through the windshield wiper switch high signal circuit. The windshield wiper switch high signal circuit is supplied 12 volts by the wiper motor module and when the wiper/washer switch is turned to the HIGH position the windshield wiper switch high signal circuit is grounded through the switch ground circuit. The windshield washer pump is controlled through the windshield wash relay. The windshield wash relay coil and switch is supplied battery positive voltage, and during WASH mode the wiper motor module grounds the washer relay control circuit energizing the relay. When the relay is energized battery positive voltage to the switch side of the relay is supplied to the washer pump control circuit.

The is the symptom of a defective wiper switch.

Lose connections , Switch , BCM - body control module , wiper control relays . wiper motor going bad etc.... Taking the vehicle to a qualified repair shop to have it diagnosed would be your best bet . Could have DTC'S - diagnostic trouble codes stored in the BCM . There is nothing commom about these systems .

The windshield wiper/washer switch signal circuits are inputs to the body control module (BCM) and the BCM controls wiper motor low speed operation, washer pump and high speed operation. The windshield wiper/washer switch is provided a low reference from the BCM and each of the switch signal circuits is supplied 12 volts through a resistor and monitored within the BCM. During LOW or INTERMITTENT operation the wiper switch low signal circuit is closed to the low reference circuit through a series of resistors within the switch assembly and the signal circuit voltage monitored by the BCM will depend on the switch contact location to the resistor assembly. During HIGH or WASH operation the high and wash switch signal circuits are closed directly to the low reference circuit within the switch assembly and nearly all the signal circuit voltage will be dropped across the BCM resistors. The BCM controls the wiper motor through the WIPER CONTROL PCB Relay and the WIPER SPEED PCB Relay. During any wiper motor function that uses low speed the BCM supplies the voltage to energize the WIPER CONTROL PCB Relay and battery voltage will be supplied from the WIPER CONTROL PCB Relay through the de-energized WIPER SPEED PCB Relay to the wiper motor low speed control circuit. During high speed wiper motor operation the WIPER CONTROL PCB Relay is energized as in low speed and the BCM provides a ground to energize the WIPER SPEED PCB Relay and the battery voltage is supplied to the wiper motor high speed control circuit. Wiper motor park operation is controlled by the BCM using an input from the park switch within the wiper motor assembly. The BCM supplies the park switch signal circuit 12 volts through a resistor then monitors the circuit. Whenever the wiper motor is out of the park position the park switch signal circuit is closed to ground and nearly all the signal circuit voltage will be dropped across the BCM resistor. When the wiper switch is turned to the OFF position while the wiper motor is somewhere in mid-cycle, the BCM will continue to operate the motor until the wipers reach the park position. If the ignition is turned OFF while the wipers are in mid-cycle, the wipers will stop immediately where they are and the BCM will park the wipers the next time the ignition is cycled ON.

DTC B3715 02: Front Wiper Relay Drive Circuit Short to Ground
DTC B3922 00: Front Wiper Function Select Circuit

Yukon what ? just a plain yukon ? 2WD or 4WD XL - Denali etc...
No pulse board . controlled by the BCM - body control module . Taking the vehicle to a qualified repair would be your best bet .
Windshield Wipers
The windshield wiper/washer switch signal circuits are inputs to the body control module (BCM) and the BCM controls wiper motor low speed operation, washer pump and high speed operation. The windshield wiper/washer switch is provided a low reference from the BCM and each of the switch signal circuits is supplied 12 volts through a resistor and monitored within the BCM. During LOW or INTERMITTENT operation the wiper switch low signal circuit is closed to the low reference circuit through a series of resistors within the switch assembly and the signal circuit voltage monitored by the BCM will depend on the switch contact location to the resistor assembly. During HIGH or WASH operation the high and wash switch signal circuits are closed directly to the low reference circuit within the switch assembly and nearly all the signal circuit voltage will be dropped across the BCM resistors. The BCM controls the wiper motor through the Wiper Relay and the Wiper High Relay. During any wiper motor function that uses low speed the BCM supplies the voltage to energize the Wiper Relay and battery voltage will be supplied from the Wiper Relay through the de-energized Wiper High Relay to the wiper motor low speed control circuit. During high speed wiper motor operation the Wiper Relay is energized as in low speed and the BCM provides a ground to energize the Wiper High Relay and the battery voltage is supplied to the wiper motor high speed control circuit. Wiper motor park operation is controlled by the BCM using an input from the park switch within the wiper motor assembly. The BCM supplies the park switch signal circuit 12 volts through a resistor then monitors the circuit. Whenever the wiper motor is out of the park position the park switch signal circuit is closed to ground and nearly all the signal circuit voltage will be dropped across the BCM resistor. When the wiper switch is turned to the OFF position while the wiper motor is somewhere in mid-cycle, the BCM will continue to operate the motor until the wipers reach the park position. If the ignition is turned OFF while the wipers are in mid-cycle, the wipers will stop immediately where they are and the BCM will park the wipers the next time the ignition is cycled ON.

There should be a printed circuit board on the motor that controls the intermittent and park functions of the wipers.

The PCB wiper relays are soldered directly to circuit board inside the under hood fuse box.
The windshield wiper/washer switch signal circuits are inputs to the body control module (BCM) and the BCM controls wiper motor low speed operation, washer pump and high speed operation. The windshield wiper/washer switch is provided a low reference from the BCM and each of the switch signal circuits is supplied 12 volts through a resistor and monitored within the BCM. During LOW or INTERMITTENT operation the wiper switch low signal circuit is closed to the low reference circuit through a series of resistors within the switch assembly and the signal circuit voltage monitored by the BCM will depend on the switch contact location to the resistor assembly. During HIGH or WASH operation the high and wash switch signal circuits are closed directly to the low reference circuit within the switch assembly and nearly all the signal circuit voltage will be dropped across the BCM resistors. The BCM controls the wiper motor through the WIPER CONTROL PCB Relay and the WIPER SPEED PCB Relay. During any wiper motor function that uses low speed the BCM supplies the voltage to energize the WIPER CONTROL PCB Relay and battery voltage will be supplied from the WIPER CONTROL PCB Relay through the de-energized WIPER SPEED PCB Relay to the wiper motor low speed control circuit. During high speed wiper motor operation the WIPER CONTROL PCB Relay is energized as in low speed and the BCM provides a ground to energize the WIPER SPEED PCB Relay and the battery voltage is supplied to the wiper motor high speed control circuit. Wiper motor park operation is controlled by the BCM using an input from the park switch within the wiper motor assembly. The BCM supplies the park switch signal circuit 12 volts through a resistor then monitors the circuit. Whenever the wiper motor is out of the park position the park switch signal circuit is closed to ground and nearly all the signal circuit voltage will be dropped across the BCM resistor. When the wiper switch is turned to the OFF position while the wiper motor is somewhere in mid-cycle, the BCM will continue to operate the motor until the wipers reach the park position. If the ignition is turned OFF while the wipers are in mid-cycle, the wipers will stop immediately where they are and the BCM will park the wipers the next time the ignition is cycled ON.

DTC B3715 02: Front Wiper Relay Drive Circuit Short to Ground
DTC B3875 00: Wiper High Speed Relay Circuit
DTC B3922 00: Front Wiper Function Select Circuit
Have it checked for DTC'S - diagnostic trouble codes .

The body control module (BCM) controls the wiper motor based on input from the windshield wiper washer switch. The BCM monitors the wiper washer switch through three separate signal circuits and a ground circuit. The windshield wiper switch high signal circuit is used to determine high speed wiper operation, the windshield wiper switch low signal is used to determine low speed, intermittent, and mist operation through the use of a resistor ladder, and windshield washer switch signal circuit is used to determine washer operation.
The BCM controls the windshield wiper motor through two output controls, controlling two relays which determine the desired wiper speed, high or low.
Your best bet , take your vehicle to a qualified repair shop or dealer . Hooking up a factory scan tool to see what the wiper switch inputs to the BCM are correct and outputs to relays are good .

Are u assuming the GEM module is at fault ? Did you or your local auto electrician check for DTC'S - diagnostic trouble codes?
GEM/CTM Wiggle Test Diagnostic Trouble Code (DTC) Index DTC Description DTC Caused By B1317 Battery Voltage HIGH GEM/CTM B1318 Battery Voltage Low GEM/CTM B1322 Driver Door Ajar Circuit Short to Ground GEM/CTM B1330 Passenger Door Ajar Short to Ground GEM/CTM B1352 Ignition Key-In Circuit Failure GEM/CTM B1410 Driver Power Window Motor Circuit Failure GEM B1438 Wiper Mode Select Switch Circuit Failure GEM/CTM B1441 Wiper Mode Select Switch Short to Ground GEM/CTM B1446 Wiper Park Sense Circuit Failure GEM/CTM B1450 Wiper/Wash Interval Delay Switch Input Circuit Failure GEM/CTM B1453 Wiper/Wash Interval Delay Switch Input Short to Ground GEM/CTM B1462 Seat Belt Switch Circuit Failure GEM/CTM B1577 Park Lamp Input Circuit Short to Battery GEM/CTM B1610 Illuminated Entry Input (From RAP Module) Circuit Short to Ground GEM/CTM
Did you an your auto electrican check power an grounds for the GEM ? Voltage drop testing ? . Did you check power an ground circuits for the affected systems . Working when they want sounds more like a loose connection somewhere .
ECM Inputs and Outputs Diagnosis
Symptom Chart
Symptom Chart Condition Possible Sources Action

• The Wipers Are Inoperative

• CJB Fuse 16 (30A).
• Circuitry.
• GEM/CTM.
• Multi-function switch (13K359).
• Wiper run/park relay.
• Wiper HI/LO relay.
• Wiper motor.
• DTC B1431.
• DTC B1432.
• DTC B1438.
• DTC B1450.
• DTC B1840.

• GO to Pinpoint Test A .

Plus looking at GEM scan data on a factory scan tool .Too many people miss diagnose these system's because they don't have a clue .

Could be anything but based on experience the probability points to the self cancelling switching in the motor gearbox.