What you likely experienced is the need to reset the Engine Control Module (ECM), sometimes called the PCM (Powertrain Control Module). A battery disconnect will often cause the ECM to store various codes that are unrelated to actual problems. These codes can cause issues like rough running, poor performance, or even a check engine light.
The ECM in your 1996 Jeep Grand Cherokee *resets itself*. After disconnecting the battery, you need to:
1. Reconnect the battery: Make sure the positive (+) and negative (-) terminals are securely attached.
2. Turn the ignition to the "ON" position (but don't start the engine): Let the system power up for a few minutes. This allows the ECM to complete its self-test and initialization procedures.
3. Start the engine: Let it run for 10-15 minutes to allow the ECM to learn and adapt to the current conditions.
Important Considerations:
* Check Engine Light: If the check engine light remains on after this process, you'll need to use an OBD-II scanner (available at most auto parts stores) to read and diagnose any trouble codes. These codes will indicate the specific problem(s) the ECM has detected. Keep in mind that a 1996 vehicle may require an OBD-I scanner, not OBD-II.
* Learning Process: The ECM needs to relearn various parameters, such as idle speed and fuel mixture, after a battery disconnect. Expect some slightly rough running initially, which should smooth out after the 10-15 minute running period.
* Other Systems: Disconnecting the battery might also affect other electronic systems, like radio presets or clock settings. You might need to reprogram those individually.
If the problem persists after following these steps, there's likely a more significant underlying mechanical or electrical issue requiring professional diagnosis and repair.
