I have a 1999 Dodge Ram 1500 Laramie SLT extended cab pickup with a 5.9L that has a p0720 code. I replaced the output speed sensor a few months back but now the code is back. Do you think the new sensor has gone bad already? Are there 2 sensors on the transmission? Where would the other one be? Do I need to replace the one on the rear diff?

Thanks

 

Only one speed sensor on the trans for you.

If the sensor is still under warranty, try swapping it out.

 

Did you clear the PCM when you did it ? Just want to make sure it's not just a stored code . If you did not , just disconnect the battery for 20-30 minutes and it's done . If the CEL reappears , maybe you did get a bum sensor . Brand ?

Only 2 sensors on the trans , nothing on the diff . 1 is the trans output sensor which feeds the speedo , the other is the trans speed sensor which feeds the PCM . Assuming you are 2wd , the sensor for that code is the farthest towards the rear of the two . I believe that's the one you replaced already .
The second sensor will be approx 7-8" back from the trans basepan and have 2 wires coming from it (red/green IIRC) . It will be more on the bottom/side . That's a magnetic pick up sensor . They do get dirty . Just be prepared for some oil if you remove it to clean .