The P0842 is for a problem with the pressure solenoid. This can be caused by something as simple as low transmission fluid or dirty fluid.
P0842 CHEVROLET - Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low
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P0700 is an information code to let you know there is a problem with the transaxle. Check the TCM for more codes, but it's likely there because of the first code.
P0700 CHEVROLET - Transaxle Control System Malfunction
Read more: http://kvjournal.ru/p0700_chevrolet.html