2008 GMC Sierra Crew Cab 1500 service four wheel light on and will not engage when four wheel drive selected. Already changed the switch no change.

 

What switch did you change? There’s an actuator in the IFS (independent from suspension) differential. When 4H or 4L is selected an electrical signal is sent to the transfer to engage the transfer and illuminate the display lamp. The circuit continues and sends a signal to the IFS actuator and that actuator (it’s a solenoid) shifts a coupling linkage inside the IFS engaging both front axles. All the IFS does is engage and provide driver to the front wheels. The transfer selector determines the ratio of 4H or 4L based on what you asked for.

Start by doing a visual inspection to ensure the harnesses are good and no breaks or damage. Then check voltages to the transfer and to the IFS with your key on and in 4H & 4L. Your IFS connector may have 1 or 2 cable connectors or be a 3 or 4 pin unit. GM cannot seem to be consistent. That connector is typically clipped to the passengers side IFS axle tube. You may need to remove the plastic Debris covers from under it.

Dont jump ahead and throw a new IFS actuator at it - they can be pricey.

 

Okay thanks for the information. I changed the four wheel drive selector switch on the dash. The light activates for the two wheel drive position but when selected for AWD FWD and FWL low ,they don't light up. I'll check for power at the IFS actuator and go from there. Again, thanks for the information.

 

Have you had a chance to troubleshoot more? Be sure to update us with all progress!

 

Have not had a chance to get to it yet... Just had replace the oil sending switch and screen. This truck hit 100000 miles and is falling apart.

 

2008 GMC Sierra four wheel drive not working with service four wheel drive drive light warning on the dash .. selector for four wheel not switching from 2wd to AWD, 4WD and low 4WD. Checked for power at front axle actuator no power. Ran direct 12 volts to actuator actuator engaged. Checked fuse and power fuse is good and have power to transfer case actuator. Does anybody know if there's a typical problem with the wiring from the switch to the actuator? Or maybe a BCM problem?

 

Hi there I have a 2000 GMC Sierra(new body style) 1500 4x4 with electronic push button 4wd with auto mode. I work in construction and need the 4x4 almost every day. A couple of times a week the 4wd doesn't engage, it just stays in 2hi, how to engage 4 wheel drive chevy Silverado or it will even go into 4hi and get stuck in 4hi. If I play with it long enough it will eventually shift. The "Service 4wd" Message will also appear quite often also. Are there problems with the 4wd actuators in these trucks?