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Q: Have fault codes of P0700 & P0158. The later has subcodes,mine 2. How serious? on 2006 Jeep Liberty

P0700 seems to be a transaxle control system fault. There are 2 subcodes; one for a short or open circuit the other a control module failure. P0158 is a circuit condition; printout of fault says (heated oxygen sensor bank aa2 sendor 2). The subcode (aa2), if reading it right, says system running rice or lean - check other codes first.
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The P0700 code indicates there's a problem with the trans. You need to have the trans codes extracted out of the computer. You can't just use a generic code reader. It has to be an enhanced scanner.

code P0158

1. Test the operation of the 2/2 O2 sensor. On this vehicle it should switch between 2.5 volts and 3.5 volts.

2. To test for a bad sensor, swap the downstream sensors side to side and check for a different code to be set.

As long as you have to find a shop or a tech with a enhanced scanner, have them look at the serial data on the downstream O2.

As for the "subcodes" there's no such codes.
To confirm, P0700 is a tranaxle or transmission fault? Went to an AutoZone and they did the check for me and printed the faults. P0700 says Transaxle System Fault; ECM received a signal that the trtansaxle control module has a fault; short or failure of the control module. What should I be looking for if scanned again with an enhanced scanner? How serious is this?

Where can I find a schematic for the downstream 02 sensors? What do you mean when you say "check for a different code to be set"?

Finally, I disconnected the neg terminal on the battery to reset the check engine light. Have driven the car about 15 miles on sidestreets and interstate, but the check engine light has not come back on. Is that significant?

First, autozone is a auto parts store, not an auto repair shop. Second, they are using a generic OBD2 code reader. A code reader will not provide the trans codes. Third, P0158 code concerns the downstream O2. Without having the ability to look at the serial data of a enhanced scanner if you change the rear O2 to the front O2 the trouble code should show for the front O2.
A P0700 does indicate you may have a trans problem. Both these codes will take time to set again. Lets hope they don't come back.
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