I am stumped!!!
 

Went out to start the 2000 Grand Cherokee today, and much to my surprise, it started and ran very poorly. The engine is misfiring badly, the instrument cluster is showing lights for the abs and brake, the voltmeter isn't working, and the "check gages " light is on. The alternator is also putting out over 17 volts. I don't understand what happened. It was fine the last time it was driven, which was last week. I have tested both the battery and the alternator, and both are fine. So, what's up with this thing???:icon_cry:

Welcome to CF!

Believe this or don't, but the problem could just be a bad connection on the battery cables. Corrosion or a loose wire from the clamp to the PDC can cause low voltage and produce the symptoms you report.

is the alternator actually charging at 17volts. because if it is thats not ok.

Welcome to the forum. Please explain the red text. Alternators should not be charging 17 volts. What were your actual readings when you checked the alternator and battery?

Take Dave's advice and check the battery cables. Check for chewed wires as well. Mice will cause havoc on wiring.

The reason I stated what I did is because this exact thing happened to me. What it turned out to be was corrosion inside the molded battery cable end causing a low voltage supply to the entire system except the starter. There are 2 red wires coming off the battery cable clamp. One goes directly to the starter and the other goes to the PDC which supplies all the power for the rest of the jeep. This happened overnight and replacing the cable end solved the problem.

PS, if the PCM can't read the alternator output, it can't control the voltage OR the amperage.

Yep, remove the terminals and clean well.

I had very similar symptoms, and it turned out to be a thin white film between the terminal and post that wasn't readily visible from the outside.

Cleaned it and it went back to working as it should.