I own a 98 F150, 4.6L, 4x4, 4R70W transmission. I had a post a few months back about a flashing O/D Light. The light only flashes after about 20 minutes or so of constant driving. Around town on short trips, nothing. When this started a few months back I pulled the code P1500. I had a few people tell me to change the sensor on the rear-end. So, I proceded to change the sensor on the rear-end. Drove for a few days, around town, so no flashing because I hadn't taken a long trip. Next day, transmission goes out. Clutch band blew apart. So, I ditch that tranny and have a new one installed. Took two months because of warranty fight. So here I am today, take a 45 minute trip and the light begins to flash again. No harsh shifts like before. No speedomenter issues like I've seen on some posts. Truck runs fine, just a flashing O/D light. I don't know what to change next. I contacted my Ford garage and they will gladly help out. Of course it will be $70 just to hook up and read the codes, which I already know. Then $50 an hour labor after that. So, anyway, trannys brand new (rebuilt) and rear sensor is new. Any thoughts. Thanks

 

How do you already know the code? Just because it set a P1500 last time doesn't mean that the same code set this time.

Casey

 

Not an assumption. I hooked up to my computer and read the code. Same code as before. I have heard several sensors can cause this problem. Besides the speed sensor in the rear-end, I am not sure what else to change.

 

I've got the same thing happening . the o/d light flashes when on the highway. I my tranny shop told me it's prob. the speed sensor gear starting to wear out or a bad wire.
I'm going to get it checked next month.

 

Hi derhicks

I think I can help with your problem. First off the sensor in the rear diff is for the abs not the vss. The vss on your year truck is in the transfer case extension housing.

There may be a fault with the sensor itself, or damage to the plastic vss drive and driven gears. The drive gear is mounted on the output shaft of the transfer case and the driven is on the vss.

Ford had problems with the drive gear becoming loose on the shaft and causing an erratic signal. Some times the gear was loose due to water contamination in the transfer case, but not always. This usually shows up at higher speeds on longer trips. Ford has released a updated drive gear for the vss that has a tighter fit, if you want the part#, let me know and I will find it.

This used to be very common, I changed too many to count. Changing the vss drive gear is fairly easy.

Hope this helps

Later

 

Xplorer,
Just wanted to give an update on the transmission situation. As I stated, rear sensor has been changed. Sensor and drive gear on the transfer case has been changed. I noticed a sensor on the transmission itself. This sensor has not been changed. Anyway, I still have a flashing light. I drove today for about 15 minutes locally at 50 MPH or less. No problems. As soon as I hit highway speeds (65MPH) the O/D light started to flash. No erratic shifts, everthing runs fine but the light flashes. I shifted the truck to neutral and restarted it while on the highway. The light goes out. Drove for another 10 minutes on the highway with no problems. Also drove for about 15 minutes around town with no problems. It seems as though a restart will always reset the light. Obviously the light is not flashing for no reason but when it does I see no change in the trucks performance. Before the transmission went out I would see erratic shifts when the light flashed. What does the sensor that plugs into the transmission itself do and could this be the trouble or might it be something more severe like a bad PCM. Any input would be appreciated. Thanks

 

Hey derhicks

The sensor that you are talking about (that plugs into case), is it on the driver side of the trans, with a two pin connector? If it is, it is the oss(output shaft speed) sensor. It would not set a code P1500.

You said you had the codes checked again and it was a P1500, so it still has a fault in the vss circuit somewhere. I will check into some older tsb's/ssm's, I seem to remember having this happen before(changed all the sensors/gears, still same problem) I just cannot remember what I did to finally repair it. I will post back when I find something.

I might need the vin off your truck to check further. I'll let you know.


Later

 

Just an update to anyone who may have followed this post. Ford suggested replacing the sensor agian as sometimes, not often, the sensor could be bad out of the box. I had changed the VSS first. Then, Xplorer suggested chaning the drive gear. Good idea since it was practically falling off the shaft. Neither the sensor or the gear being changed stopped my light from flashing. So, I followed Fords suggestion and put my old sensor back on. O/D light stopped blinking. I have 250 miles since the switch and no problems. Apparantly, the gear was the problem from the get go.
Thanks for all your input Xplorer.

 

derhicks
Just out of curiosity when you pulled the vss out how much play did you have on the gear? Mine isn't falling off but it isn't a tight fit. Just a little side to side. I'm chasing the same problem you had. I had a p1500 and p0503.
Rob