I have a 1999 Dodge Ram 318 with 110k miles on it. Yesterday my check engine
light came on. As I was driving to the auto zone I noticed a difference in
the 4 speed automatic trans. It seemed to have trouble shifting from 1st to
2nd. It stayed in 1st gear longer. The tech at Auto Zone read the Codes and
came up with error code P0720. The definition was A low speed sensor speed
above 15 mph.
Explanation was Vehicle speed above 15 mph while transmission output shaft
speed below 60 mph.
1. Failed output shaft speed sensor
2. Electrical problem.
Where is the speed sensor? I sure hope it is on the outside of the trans.
Any help on this? Thanks
Yep, it's on the outside. Look for a two-wire sensor at the back end of the
tranmission, driver's side, in the overdrive unit. You unplug the wiring,
and screw it out of the housing. Make sure the O-ring comes out with it.
You should get a new O-ring with the new sensor. Lightly lube the O-ring
with ATF, and re-install the sensor. You'll probably get some fluid leakage
when you remove the old sensor. Have a pan ready to catch it, be ready to
quickly replace the sensor with the new one, and then dump the caught fluid
back in through the dipstick (goes without saying... use a clean pan to
catch the fluid).
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