1999 Jaguar XJR, 80K miles.

I went to go start my car this morning and it has been colder than it has been, but still not obscene, 25F. When I put the car in gear, the car had a hard shifting lurch and then displayed trans fault on the dash. I restarted the car and the code was clear.
The car seemed to drive fine at first and then noticed that it was probably in limp home mode. Acceleration was very sluggish.
On my drive home from work, it was accelerating better, but it seemed not to kick down shifts, and was revving higher than usual.
I plan to not drive the car again until I can get this resolved.
I checked fault codes with my reader and came back with P0730 Incorrect Gear Ratio & P1797 CAN transmission control unit to engine control unit malfunction.

I have not checked the trans oil, but given the low miles, I doubt it's ever been serviced. I have also read that the P0730 code might be able to be fixed by a jag dealer reflash & learn process.
What would be the least costly course of action to get this resolved. It's a beautiful car in otherwise great condition.

 

Start with checking available battery voltage. Use a voltmeter to measure the voltage across the terminals with the ignition in the OFF position. There should be a minimum of 12.6 volts available. If not, charge the battery for five hours at 3 to 5 amps and retest. If the voltage is still less than 12.6 volts, the battery is suspect and should be replaced prior to making any further diagnosis.

 

Also check the voltage on the battery terminals while the engine is running (should be ~14 volt) to eliminate the alternator.

 

Replaced my battery with a known good one. Cleared the code and it hasn't come back since. Crazy how sensitive these cars are to minor electrical variations.
thank you. Glad i don't need a new tranny