Diagnostic Code 12 on a 1995 Grand Cherokee just means that your battery has been dead or disconnected within the last 50 ignition cycles.
The check engine light on a 2005 Jeep Grand Cherokee looks like this... Here is a link Check Engine Light It looks like a little yellow engine.
A flashing check engine light normally means you have a misfire.
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
Disconnect the negative battery cable for about two minutes and that should reset your check engine light.
May want to check flexplate, could be cracked.
Misfire? Due for a tune up? Check engine light on?
That totally depends on engine size. Check the VIN numbers and cross reference the transmission by using one of the available VIN number decoders online.
Check fan relay
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
probably u-joints on driveshaft
That is the check engine light.
If your Jeep grand Cherokee Snatches when you are driving, kindly take it to a professional mechanic to check it out for you.