* Transmission Issues: This is the most probable cause. Several transmission problems could lead to this:
* Low or No Transmission Fluid: Check the fluid level immediately. Low fluid can cause catastrophic damage. If it's low, you need to find out *why* it's low (leak, etc.) before driving it further.
* Transmission Failure: Internal transmission components (gears, clutches, etc.) might have failed. This is a major repair.
* Transmission Solenoid Problems: These electrical components control the fluid flow within the transmission. A faulty solenoid can prevent gear shifting.
* Torque Converter Issues: The torque converter connects the engine to the transmission. Problems here can prevent power transfer.
* Driveshaft Problems: A broken or severely damaged driveshaft prevents power from reaching the wheels. This would typically involve a loud noise prior to complete failure, though.
* Transfer Case Problems (4WD Models): If it's a 4WD Suburban, issues with the transfer case can prevent power transfer to the wheels. A common problem is a low transfer case fluid level or a damaged component inside the transfer case.
* Differential Problems: Problems within the front or rear differential (depending on whether it's 2WD or 4WD) can prevent wheel rotation. This often involves a loud noise before complete failure.
* Parking Brake Engaged: Sounds obvious, but make sure the parking brake isn't accidentally engaged.
* Electrical Problems: Though less likely to cause a complete inability to move, a problem with the neutral safety switch (prevents starting unless in Park or Neutral) or other electrical components related to the transmission could be involved.
Troubleshooting Steps:
1. Check Transmission Fluid: This is the first thing you should do. Check the level and condition (color, smell).
2. Check Parking Brake: Ensure it's fully released.
3. Listen for Unusual Noises: Any grinding, whining, or banging noises during attempts to move the vehicle can provide clues.
4. Try Shifting Through All Gears: See if you hear or feel anything unusual when shifting.
5. Check the Engine: Make sure the engine is running smoothly and not overheating. A serious engine problem could indirectly affect drivetrain operation, although it is less likely to lead to an *immediate* complete failure of forward and reverse.
Important: Do not attempt to drive the vehicle if you suspect a serious transmission problem. Towing it to a qualified mechanic is the safest course of action. Driving it could cause further, more expensive damage.
