1. Power Supply Issues:
* Battery: Start with the simplest: Check the battery voltage. A weak battery can cause intermittent or complete failure of electrical systems. Test both voltage at rest and while cranking the engine.
* Fuses and Relays: Check the fuses and relays related to the power windows and central locking system in the fuse box (usually under the hood and inside the cabin). The owner's manual will show fuse locations and ratings. Look for blown fuses or damaged relays (corroded contacts, clicking sounds). Replace any faulty components.
* Wiring: Look for any obvious damage to wiring harnesses, particularly those running to the doors (common wear points from opening and closing). Look for breaks, chafing, or corrosion. This can be tricky; you might need a wiring diagram.
2. Central Locking System Issues:
* Central Locking Module (Body Control Module - BCM): This is a common culprit. The BCM controls many electrical functions, including the power locks and windows. A faulty BCM needs replacement, which can be expensive. A mechanic with diagnostic equipment can test the BCM.
* Actuators: The door lock actuators themselves could be failing. If the manual lock still doesn't work, the actuator itself is likely the problem. Testing this usually requires removing the door panel.
* Wiring to Actuators: Check the wiring running from the BCM to the door lock actuators. Damage or disconnection in this wiring will prevent operation.
* Remote Transmitter Battery: While unlikely given the windows are also out, replace the battery in your remote control just to rule this out.
* Security System Interference: If your Jeep has an aftermarket alarm or security system, it could be interfering with the central locking system.
3. Power Window System Issues (separate but often related):
* Window Motor/Regulator: Though unlikely to fail simultaneously across all doors, a faulty window motor or regulator in one door *might* be drawing too much current and causing a system-wide failure due to a fuse or BCM overload. Check each door individually.
Troubleshooting Steps:
1. Battery Test: This is the first and easiest step.
2. Fuse and Relay Inspection: Check all relevant fuses and relays.
3. Visual Inspection of Wiring: Carefully examine all wiring harnesses for damage.
4. Check Manual Door Locks: If the manual door locks also don't work, the problem is *likely* not the remote or its battery.
5. Consult a Repair Manual: A Jeep Grand Cherokee repair manual will provide wiring diagrams and troubleshooting information specific to your vehicle.
6. Professional Diagnosis: If you can't identify the problem, take the Jeep to a qualified mechanic or automotive electrician. They have diagnostic tools to pinpoint the fault, potentially saving you time and money on unnecessary part replacements.
Important Note: Working on car electrical systems can be dangerous. If you're not comfortable working with electricity, it's best to take your vehicle to a professional.
