I'm new to this forum, so you'll have to excuse me if this has been posted before.
I have a 2001 F250 Super Duty with a 5.4L engine, regular cab. The truck has 149000 miles on it. I bought it about a month ago and had the transmission rebuilt, the spark plugs and coils replaced. Apparently the shady dealer I bought the truck from had power washed the engine and there was water in 3 of the spark plug wells on the drivers side. When I got the truck back from the transmission shop and backed it out of the parking lot, the OD off light started flashing and the SEL light came on. The code showed to be a P0720 to which the mechanic at the transmission shop replaced the speed sensor on the top of the tranny. He said if it comes on again then the speed sensor on the rear differential could be the problem and that he would have to charge me to replace that sensor since it isn't covered under the warranty for the transmission.. I replaced the sensor myself on the rear differential yesterday and thought the problem was fixed. I drove the truck around for 30 minutes with no problems, until I put the truck in reverse, then the OD off light started flashing and the SEL light comes on giving the same P0720 code. Can anyone shed some light on this?

Thanks so much
Janie

 

He led you down the wrong path. The P0720 code can only set from a problem with the output speed sensor located on the transmission. The sensor in the rear axle can't set that code.

The code means either the sensor is bad OR the wiring to the sensor is bad. Since they already replaced the sensor I'm betting on the problem being in the wiring. The output sensor is on top of the transmission at the rear end of the trans. It has a two wire connector plugged into it. The other end of those wires connect to the PCM. One or both of those wires is going to have a problem.

 

Thanks for the information Mark....I'll definitely check that out and let you know what I find.

 

Well....I took the truck back to the transmission shop and let him know the situation. He was very helpful in trying to find the problem. He put a new solenoid pack, another new speed sensor, changed the oil and checked the gears in the rear differential, checked all the wiring including the wiring for the Overdrive switch. Everything appeared to check out ok with all of the wiring. He was still getting the overdrive off light flashing....he had the PCM re-programmed and that seemed to have fixed the problem...or so he thought. As soon as I picked the truck up and put it in reverse, the Overdrive off light started flashing again. I read somewhere else in this forum where someone had the same problem and they had tried everything I've mentioned here, and finally they replaced the negative battery cable. What does the negative battery cable affect? Could this be my problem, and how difficult is the cable to change out?

Thanks so much!

 

This thread is really old, but I thought it most fitting to post my issue here. I also have a 2001 F 250 with the 5.4 with the exact same problem jgardner1227 was having. I hope he is still around so he can explain how his issue was resolved. First I had both OSS and VSS sensors replaced, then had tranny rebuilt. Overdrive light continued to flash, followed by a 0720 and sometimes 0722 code. Replaced plugs and installed new coil boots. Still flashing. Truck runs very well most of the time. Problem seems intermittent and it does not seem to happen unless the truck if fully heated up. If I warm it up for an extended time in the driveway, it will do it right when I take off. If I start out cold, it won't do it until I've been driving for quite some time and then have to stop for a minute, like at a stoplight. When I begin to accelerate from stop, the O/D light will start flashing, the truck will sputter a bit, check engine light comes on, throws 0720 code. Once up-to-speed at higher RPMs the O/D might continue to flash, but everything feels fine. Tranny shot got it to do it while it was on their lift one time and said one of the two sensors was jumping all over the place. Tired of throwing money at this. Someone please help!