Hi all , I need help please, I have been getting the dreaded flashing OD light on the shifter, trouble codes P0720; P0722 religiously. I have replace both input and output speed sensors on the transmission, the transmission range sensor, the rear differential speed sensor and the transmission solenoid pack within the transmission , the alternator, looked for damage to the wiring harness and I’m STILL getting these codes! I’m sooooo sick of throwing money at this POS and getting nowhere for a solution. The transmission shifts fine in all gears , no slippage. When the OD light starts flashing the engine stalls as soon as I put it in any gear. Has ANYONE ever run into this nightmare before and if so please for the love of GOD tell me how to fix it before I go blow this POS up! I bought it private sale from what I thought to be an honest man but come to find out he hid ALL the issues it had and ran with the money. The ONLY thing I haven’t replaced yet is the Computer and I’m gun shy to spend anymore money on this turd without confidence in fixing it. I could use a miracle right about now please ANYONE!

 

It helps to let us know more about your vehicle - I'm going to guess 2001 from your screen name, but gas/Diesel, 4x4/4x2, and sometimes trim level can make a difference when troubleshooting electrical issues.

Also, any modifications, like a chip or or any nonfactory add-ons.

 

Hi there, sorry for the lack of info . It’s a 2001 Excursion 6.8L v10 gas 4r100 transmission 4x4.

 

Okay. How many miles? Have the COPs been changed recently?

One of the "suspected" cause of the OD light and related codes is transient AC voltage, which some have traced to the COPs and/or alternator. Since you have replaced the alternator, you may try unplugging one COP at a time and going for a test ride - it will run very slightly rough, but it will be fine otherwise. Do this, one COP at a time, testing... see if the OD light goes away. If it does, the disconnected COP is suspect.

It gets more complex if it's more than one COP, and if you have more than 100k on the truck, it may be in your best interests to do plugs and COPs anyways. Some say they last and run flawlessly until they're dead, others replace them at specified intervals.

Another universal issue is the overdrive switch wiring itself, an easy fix:

https://www.ford-trucks.com/forums/1...l#post10816430

https://sites.google.com/site/woodnt...attredirects=1

You have a solid rig, keep at it and you will find the problem.

 

I looked up your codes in the Ford Factory service manual and followed the pin point test “F”
if you had Forscan you could verify some results and further flush out the causes but without being able to verify which sensor does or does not have have signal you will just need to poke around and find the short. As mike pointed out above and linked to the common ones that is where I would start. If the usual wire break spots don’t reveal your short then get Forscan and I will post pics of the pin point test in the manual

 

Hi again , yes all the cops have recently been replaced and I just went through testing all ten just now, none of the cops were causing the problem. However just for kicks I unplugged the alternator and I tried to replicate the problem MANY times and could not get the codes to re appear while alternator was unplugged. As soon as I plugged the alternator back in the issue came back almost immediately. This is puzzling to me because the alternator is new. So at a last ditch effort I dismantled all the connections to the battery and the alternator and went through and cleaned and re assembled all connections as well as chassis ground off the firewall. I tried it afterwards and I couldn’t make it fail again. It seems to be very intermittent. I checked the voltage coming from alternator to the battery and it is pushing 13.69 volts and pretty close to the same under a load. I’m not sure how to test for rf noise coming from alternator. So I’m going to take it for a beat and see if it returns again. I find it extremely hard to believe a new alternator is causing this but who knows, life is full of surprises . I’m hoping that something as little as cruddy connections could be the culprit. I certainly appreciate everyone trying to help me out because I’m gonna go frigging bald over this beast giving me a hard time.

 

Starting with a healthy electrical system is paramount, if you don't have good voltage output and aren't confident of your connections/grounds, there is always that chance it's something simple when you *think* you have solved the problem. With the age of these vehicles, it's never a bad idea to go through the connectors and grounds.

13.7 sounds a little low, but I don't know what the normal is for a V10 alternator. Others will chime in.

Intermittents are the classic sign of a short to ground or open, and can be a challenge to find. I am already bald.

 

Yeah I thought 13.7 seemed a little suspect from my end as well. I can’t be certain about the alternator’s health because I wasn’t the one who had it replaced. It was the previous owner, I can only guess it was recent before he dumped it because it still looks fairly recent of a change out. Love your bald comment reply ! Lmao! I’ve heard many say that it’s VERY RARELY ever a PCM failure and I don’t wanna just go buy one just to rule it out, that’s just wasting money on a what if ... ESPECIALLY if it’s something really simple but undiscovered. I don’t want to bring it to Ford because I’m all set with donating my left nut to pay for their rates for diagnostics.

 

The 13.7V sounds low to me too, for giggles see if this might be your problem.

Check the voltage again while running and see if you get a reading while on AC instead of DC. While tinkering around a little while ago looking for the cause of a drain that was killing the battery, I saw sometimes the diodes in the alternator will short. I checked and it was the culprit. On a test drive a week before I had the flashing OD light with your 720/722 codes. Have not had the issue since replacing the alternator, may be unrelated but it might be and only takes a second. New alternator I installed puts out 14.13 volts.

 

I will absolutely look into that and possibly swap out the alternator merely because I am not sure the history or quality of the one that’s currently in it. Looks like a knock off remanufactured brand at best. I will most definitely let you know what I find with this option thank you for the suggestion!

 

Don't skip cleaning and greasing both ends of the grounds. I think you're on the right track - I was going to suggest doing the AC test.

 

The female connector into the back of the alternator is often the culprit, the terminals get hogged out and do t make a tight connection, be wary of the el cheapo ones, I have seen them bad when new......stick with Motorcraft on your pigtails, connectors and all sensors.

 

Thank you for the information and recommendations on the motorcraft parts. I will definitely do that as well as look at the connectors for sloppy fit in the alternator. The alternator that the person before me that owned this truck had installed a REMY brand alternator. I suspect this is a crappy brand as I have never heard of it until recently and when I did research into it I discovered that the core for the old alternator is worth more than a new REMY brand costs to buy. That alone speaks volumes to me lol

 

I understand your guess of replacing the OSS, but why would you replace the TSS, the range sensor, the rear speed sensor, and the solenoid pack? Both codes indicate a problem with the OSS. P0720 says that there is an electrical fault with that circuit. 99% of the time that is caused by a damaged or corroded wire between the OSS and the PCM. If you haven't checked that circuit electrically, not visually, you are most likely missing the problem.
You're learning that randomly changing parts is very frustrating, wastes a lot of time and money, and rarely fixes the problem. I don't think you've checked the wiring yet (visual checks don't work so I don't count that as checking the wiring) so that's the thing to do next.

 

The other parts not associated with current codes were replaced due to other codes that used to be present as well. The two codes I’m referring to now were not part of the diagnosis of the other sensors replaced. This has been a long process of knocking out issues and trying to eliminate all codes. I’m currently only down to these last two codes which I created my post about. The solenoid pack and other sensors you are referring to with question all had their own codes presented. They are no longer issues coming up. I hope this answers your confusion as to why all others were replaced.