I have an 01 F350 7.3 PS with 152000 miles. When first starting out with a load, the light starts flashing and the engine drops to an idle rpm but does not die. Have replaced the VSS. Had same problem. Took to dealer. They confirmed a code P0720 and replaced the OSS Sensor. Took vehicle home, tried same scenario and of course still have the same problem. Does anyone know what the Code P0720 indicates or have any other suggestions?

 

According to my shop manual, P0720 indicates an insufficient output from the OSS sensor, and says it will set DTC and flash the OD light.

 

P0720 OSS Insufficient input from OSS sensor. PCM has detected a loss of OSS signal during operation.

If they have replaced the sensor it could be an intermittent short or corrosion in a connector.

 

po720 is the output speed sensor malfuntion.check this post out from one of the more informed members here.

Output Shaft Speed (OSS) Sensor

The output shaft speed (OSS) sensor is a magnetic pickup that provides transmission output shaft rotation speed information to the powertrain control module (PCM).

The output shaft speed (OSS) sensor is mounted externally on the top of the transmission extension housing. The PCM uses the OSS sensor signal to help determine electronic pressure control (EPC) pressure, shift scheduling and torque converter clutch (TCC) operation.

__________________
Alan
2001 F-250 7.3L Auto 4X4 S-Cab LWB
* My Truck * Common Mods and Maintenance * Roadside Help Network * Powerstroke Part Numbers * International - Ford X-Reference * AutoEnginuity Help * FTE "Folding@Home" Team *

 

Seems to me its a different sensor than the one on the pumpkin

 

It is there are 3 sensors on the driveline

TSS - Turbine Shaft Speed - Input shaft - Top front of tranny
OSS - Output Shaft Speed - near tail housing
VSS - Vehicle Speed Sensor - Rear pumpkin

 

Thanks for the info. Whats interesting is it only happens when I first start out. Once you are going, even if you have to stop & start if traffic, it does not do it.

 

Hello everyone!

I suspect RFI, affecting the OSS signal to the CPM. I will post the actual PCM rationality test, by friday, it will help you understand what the PCM looks for before setting the code.

Possible sources of strong RFI are the alternator, Battery cables corroded, fuel pump faulty, and any other wire running next to the returning wiring harness, the return signal from the OSS signal is tied to your transmission solenoid, TSS, and a few other electrical systems, any of them will send an unwanted voltage that can interfere with the signal, I will try to find the electrical skematics that will pinpoint areas of interest, to inspect.

 

Thank you for the info. We found that the alternator was the problem and it was interferring with the signal to the sensor. Replaced the alternator and everything works great.

 

Thanks for posting the fix.

 

I know I know.. OLD THREAD...I am having the same issue. Put a multimeter to the battery running the truck on idle and got 12.80ish volts. never got higher that 12.95.

I am thinking my aletrnator may be the issue as well.

 

I'm having the exact same problem. (Heavy loads starting out.) However my dealer says they can't connect to my main PCM and therefore can't pull any codes. They want $1,000 to replace the PCM and then go from there.

 

How did you diagnose the alternator problem? Thanks!

 

Just had same exact problem with an 03 excursion v10. Had the p0720 code and dying at stops. Unplugged alt and still same problem. Noticed a miss every now and then, put it on a scope and found one coil bad, replaced it and all is good. Never through a missfire code at all but kept getting the oss code.