Engine/Transmission (1998.5 - 2002) Erratic Speedometer and P720 Code

[apat]

Last night on my trip from Baltimore to Pittsburgh, my speedometer started to occasionally "jump around". I made it to Pittsburgh fine but the truck didn't seem to drive right. This morning I made the 5 mile trip to the jobsite and it ran fine. I had a few minutes so I decided to check for any codes by using the 3 click key method. It displayed P-720.



I've been able to find out that a P-720 code deals with the output speed sensor. My question is, has anyone had this problem? Where exactly is the OSS? What is involved in changing it?



As I said, I'm not home so I don't have access to my shop manual. I can get tools and there are numerous auto parts stores around.



Any help would be greatly appreciated. I'd like to take care of this ASAP as I'll be heading home Thursday after work.

 

[B.G. Smith]

The sensor that sends signal to the speedometer is located in the top of the rear differential housing at the center. There is on small cap scrw holding it in place. If you have a chance you should remove and inspect it, it is magnetic and might have metallic particles on it. bg

 

[Cosmo]

700 codes are typically transmission codes. I would think that the differential speed sensor would be more of an RWAL code.

The 720 is referring to the transmission output speed sensor, which should be in the overdrive extension housing. It should just screw in from the outside.

 

[Cosmo]

FYI, a 95 2500 (gas) 4x4 came into the shop today, speedo inop. I put a new speed sensor on it. It was the output speed sensor on the left side of the transfer case. It had an updated connector so I had to cut and splice, but the new connector had the same color coded wires.