2002 GMC Yukon. Front wiper only works on high speed. Where should i look first? I have looked for fuses and they all appear fine.

Remove the speed sensor and look in the hole, are there teeth in there and do they move with the vehicle, this really sounds like a speed sensor problem so if all appears good including checking the wires with a continuity tester get a new sensor.

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.

WPR/WSW fuse 25amp is located in the under hood fuse box . This a complex system ,controlled by the BCM . If you find that the fuse is good i suggest you take it to a qualified repair shop . This wiper / washer system has the capability to set DTC'S - diagnostic trouble codes !
DTC B3715 02: Front Wiper Relay Drive Circuit Short to Ground
The Body Control Module (BCM) monitors the control circuit of the WIPER relay. The voltage level should be low while the WIPER relay is de-energized and near system voltage when the relay is energized. After the BCM receives a low, intermittent, or mist signal from the wiper/washer switch, it responds by applying battery voltage through the WIPER relay control circuit to the coil side of the relay, energizing the WIPER relay.
DTC B3873 00: Front Washer Relay Circuit
DTC B3875 00: Wiper High Speed Relay Circuit
DTC B3922 00: Front Wiper Function Select Circuit
I really don't think this is a fuse problem , but if it is a blown fuse they don't just blow for no reason . Low resistance high current flow ,short to ground .
The wiper / washer switch is a input to the BCM - body control module . Depending on switch position the BCM will energize a relay the WPR relay or the WPR HI relay .

Hi, You have a blown fuse. Look in fuse box located under left dash by left knee. If not there look under hood near battery. Replace the fuse Good luck.

I am having this same problem. Fuses are fine but the wipers only work on high speed. Did you get yours fixed?

Problem with blower motor is the blower motor resistor. They are usually located next to the blower motor, a couple of screws and a couple of plugs and your done. Autozone sells them for around $30 each. Wipers you may want to check for relays under the hood in the fuse block. There may be 2 relays 1 for low and 1 for high. I have switched relays from other working accesories and got wipers to work. Sometimes bad connection.

JUST PUT A NEW GROUND WIRE TO THE REAR WIPER MOTOR............SIMPLE GOOD LUCK

You mean ecm b fuse, it is in the engine compartment fuse box , look on the left fender firewall , black box labeled fuses and relays... flip lid over it is labled for you to reference...hope this helps...thanks

its the fuse inside the fusebox under the hood. the box is right in front of the battery. I had the same problem. 4 dollar part. look it up in the owners manuel and your good to go.

check you antifreeze level and make sure its full