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Hello everybody, recently I have had my tcm replaced after a previous issue of the car giving me a hard jolt at high speeds. That problem is solved after the tcm repair, but now I have an issue where the car refuses to shift into 5th gear. The car on the highway stays in 4th at 4K rpm and won’t budge to 5th. I plugged in the computer and the P0720 (Output speed sensor circuit) code came up. This is the only code I have. Is it the actual sensor or bad wiring? The tcm was just replaced so that is my last resort as the issue.
 

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Was your replacement TCM a brand new unused unit form the dealer, or was it a used unit from the salvage yard, or was it a "rebuilt" unit from an online shop? If it was anything other than a brand new unused unit, then it could definitely be the cause of your output speed sensor circuit (P0720) code.

Do you still have the original (faulty) TCM that was causing the hard jolt issue? If yes, then you might want to re-install it and see if the hard jolt returns AND if the P0720 code remains or goes away.

The other 2 possibilities for the P0720 code could be (as you mentioned) either the output speed sensor or the wiring from the sensor to the TCM. The output speed sensor and your car's vehicle speed sensor (VSS) are the exact same part and so you could swap those 2 sensors and see if the P0720 code (OSS) remains or if you get a new code related to the VSS (like a P0500). If the P0720 code (OSS) remains then you would know that it wasn't due to the OSS, but must be due to the wiring or TCM.


Note that for all of the above tests, the cause might be intermittent and so you might have to drive it awhile until something shows up.
 
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