4R100 Computer issues
 

Rebuilt trans back in March at local shop...around June/July overdrive light started flashing and had to run up the R's to get the trans to engage at a couple of lights...took it back to the shop had them check it out..said it was a sensor in the rear end causing issues changed it no cost to me :D
Worked great....till late Sept. same issue came up again...got it in there last week and they haven't found the problem..couple phone calls and they keep saying they're not finding the issue...well yesterday I call and they say it's a computer issue and it's going to have to be replaced...they know I can't pitch a bunch of money so he's been looking for a used computer with no luck...Is this something that's heard of ...or can this computer issue be solved with a flash or reprogram or something...I don't have the codes...but I can call him and get the info...
2000 F250 239K 4R100

Get the codes and post them here.

It's never something the shop did wrong. lol

Rick, two codes T0720 and P1501.. thanks

Should the "T" on the first code be a "P"?

Both codes are for the VSS. Check the connection to be sure it is clean and not bad. I would change the VSS again before I changed the PCM.

EDIT: NAPA has the sensor for under 30.00 and they call it the ABS sensor.

they tried that first and again been getting the same codes...went through all the wiring and the trans is getting signals that it's not shifting properly and they say these inputs are coming from the computer...

I don't know much about our trans and that is why I had BTS build mine. Hopefully one of the trans guys will chime in.

Mark k. might see this and help you out.

Good luck.

That should be P0720. It's for the output speed sensor on the transmission. The P1501 is the vehicle speed sensor.

P0720 relates to the sensor on the top of the transmission at the rear of the trans. It could be a bad sensor or a damaged wire or bad connector between the sensor and the PCM. It is not at all related to the vehicle speed sensor (VSS.)

Inputs don't come from the computer. Inputs go TO the computer, output come from the computer.

While it is technically possible for a P0720 to be a bad PCM, I've never seen that happen. It has always been a bad sensor, a wiring problem, or a damaged tone wheel inside the transmission.

Mark,
Do you think there is any chance these issues could be caused by corroded connections at the battery cables? I have seen a couple of trucks that had shifting and/or tc lock up issues and cleaning the connections appeared to correct the problem. However, in both of those cases the OD light was not blinking so perhaps the OP has a different issue. :confused:

That is a possibility.

Another possibility I just remembered is that a failed rectifier in the alternator can cause bad readings on speed sensors. A bad rectifier in the alternator puts an AC voltage in the system and the PCM reads that as a bad speed sensor. You can see the problem with an oscilloscope. The AC voltage stands out and is easy to diagnose with the right equipment.

I've fixed a couple of speed sensor problems by replacing the alternator.

Great info! That explains a lot and makes perfect sense how that could be a possible cause of these issues. :-X22

Mark,

Great tip on a bad alt rectifier causing speed sensor problems.

Rep to you.

To the OP.

Pic of where the TSS and OSS sensors are. TSS - Turbine Speed Sensor. OSS - Output Speed Sensor

https://www.ford-trucks.com/forums/a...8&d=1272123563

Mark, I have heard that these two sensors are the same part number. Is that true?

Nice illustration. And a PTO case to boot...:-X22

I don't know. I do know they are electrically the same.

Thanks Mark.

I've got a friend at the local Ford dealership parts counter who can find out. I'll post the answer.

Would be nice to carry one spare to cover two parts.

Robin, The sensors are the same on a non PTO trans, but the TSS is shorter on a PTO version, as it reads off the PTO drive gear instead of directly off the Coast Clutch drum.