Bought a 2002 GMC Yukon that seems to be well maintained and runs well. it was hit in the left rear quarter lightly and it seems the load leveling system is maxed out because the back of the truck seems to be higher than the front. The truck has a bad vibration while accelarating from 40 to 70 mph and goes away when letting off the gas pedal. wondering if it may be the load leveling system causing the vibration or maybe bad ujoints

happened out of the blue now? or bought it like this?>
yukon , or yukon xl1500xl or xl2500 ? i guess left own here.
check fuses
and scan the car.
I am sure the scans will fail with DTC, so scan it see what fails.
check PS fluid levels and
for PS hoses leaking,
check loose belts to PS pump pulley
or have real shop look at it??? auto repair shop, even ASE rated shops, USA??
guess 3, hydro-electric- steering option in place, ?and or.
got rear wheel steering option?
find the, RPO code tell what it is there read RPO yet? (as built list)

read the service manual here on steering, a very complex system
check it out.

https://eautorepair.net/Marketing/Default.asp

Take it to your local parts store. Most will check the codes for you for free. Once you have the codes, you can look them up and see what's likely wrong.

Try to back wash the heater core first if it doesnt work then its clogged up try to turn the heater on the front with the heater off for the back keep an eye on the temp guage if it goes up than normal then its clogged....

Fyi u have to run the engine for awhile with the heater fan on

Would need to know what DTC'S - diagnostic trouble codes are stored in the module for the autoride suspension . Hooking up a professional type scan tool ,looking at input data to the module etc... Looking at a wiring diagram an testing electrical circuit's using a DMM - digital multi-meter . Reading how the system works ,what all involved in making the system work . This is how a professional Tech would go about diagnosing this .

The automatic level control (ALC) system maintains a desired rear suspension position under all types of towing, hauling and loading conditions. The following components are involved in the operation of the ALC system:
• Air line tubing--Pressurized air from the ALC compressor is pumped to each of the rear shocks via air line tubing.
• Air drier--Pressurized air from the compressor is run through a drier containing a moisture absorbing chemical preventing water accumulation in the rear shocks.
• Compressor--Supplies pressurized air to the rear shocks
• Compressor motor relay--The relay supplies battery positive voltage to the ALC compressor motor.
• Pressure sensor--The electronic suspension control module (ESCM) module provides a 5-volt reference and low reference to the ALC pressure sensor. The module receives the signal voltage that is relative to the air pressure applied to the rear shocks.
• ESCM--Controls the ALC system and electronic suspension control (ESC) system and detects failures in both. The module monitors inputs from the position sensors, and pressure sensor to determine when to raise and lower the vehicle to trim height as the vehicle is loaded or unloaded. The module limits pump activation to 255 seconds to prevent thermal damage.
• Exhaust valve--An electric solenoid activated by the ESCM to vent air pressure from the rear shocks.
• Left and right rear suspension position sensors--The module provides a 5-volt reference and low reference to all 4 of the body-to-wheel suspension position sensors. The sensors send the ESCM a signal voltage that is relative to the rear suspension ride height
• Left and right rear shock absorbers with internal air chambers and dampers--Dampens the rear suspension and maintains trim height depending on the air pressure applied.

These trucks are well known for faulty rear tail light circuit boards.Replace the circuit board with a new one from GM.The after market ones are junk.

Typical gm problem, the float assembly or a ground wire, Ive always run across it being the float which can be bought through the dealer seperately than the whole pump w float assembly.

2002 GMC Yukon Car Stereo Wiring Guide
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

rate pls

BLACK - GROUND (-12v)
YELLOW - IGN (+12v WHEN CAR IS ON)
ORANGE - MEMORY (+ 12v ALWAYS ON)
GRAY - BACKLIGHT (ON WITH DASH LIGHTS)
BROWN - DIMMER
PINK - POWER ANTENNA (MAY NOT BE THERE)
LIGHT GREEN/DARK GREEN - RIGHT FRONT SPEAKER +/-
TAN/GRAY - LEFT FRONT SPEAKER +/-
DARK BLUE/LIGHT BLUE - RIGHT REAR SPEAKER +/-
BROWN/YELLOW - LEFT REAR SPEAKER +/-

Use a voltmeter or test light to tell the difference between the gray dash light wire and gray speaker wire, and yellow power wire and yellow speaker wire.

check you antifreeze level and make sure its full

Check the connections from the back maybe its connect good.