My 2001 F250 showed the have engine serviced soon warning. I checked the codes and got nothing. I took it to my mechanic They found the PO 720 and 722 codes, (output speed sensor circuit fault, output speed sensor no signal). I bought an output speed sensor and am trying to replace it. The bolt holding the sensor in place is stuck. An 8mm closed head wrench fits over it, but slips as soon I try to loosen the bolt. A 7mm wrench won't fit. I can barely see the bolt, as it sits on top of the transmission on the passenger side near the front differential. I had to take the front drive line off,remove the support bracket beneath the transmission, and lower the transmission on a floor jack just to get access to where I can see the bolt using a mirror.
Am I using the wrong type wrench? Any suggestions will be appreciated.

Thanks,

Randy

 

It is an 8mm. Find a six point wrench or socket to remove it.

If the new sensor doesn't fix this come back here and I'll give you the next steps to find out what's wrong.

 

Thanks Mark. I had to get a bolt extractor to remove the bolt. I was a little hesitant because I really didn't want to have it snap at the head. Anyway, the bolt is removed, I bought a replacement bolt, and hope to have it all back together on Wednesday. I will post either way regarding the new sensor and if it solved the problem or not.

Randy

 

I finally finished the sensor replacement and had a chance to see if it solved the problem. At first, it seemed like all was well. The truck ran fine, no transmission issues, no dying at idle. I cleared the codes, then checked again for any trouble codes and found none. I am using a BlueDriver code reader. I drove the truck a couple of times, and after about 45 minutes of stop and go in town driving with a couple of stops it lurched at a stop sign and the check engine light came on. I continued to drive (as I was on my way to the dump with a trailer to empty), and it drove okay except for losing rpms when stopped at red lights. I compensated for that by shifting to N and giving it a little gas to keep the rpms up above 700 and had no problem. In addition, the Overdrive Off light on the gear shifter started flashing, even though I had not pushed the button.I replaced the gear shift lever last summer, and had no problems until now.
I read the codes when I got home and it is showing PO720 Insufficient input from Output Shaft Speed Sensor.

It lists 4 possible causes: OSS connector damaged (it looked ok when I switched out the sensor), OSS has failed (I just replaced it), OSS signal circuit is open shorted to ground, or shorted to voltage (how do I check this?), PCM has failed (would there not be other symptons indicating this is the case?).

The top report fix is to replace the coil on the plugs.
The next 7 frequently reported fixes are: replace ignition coils, replace spark plugs, replace alternator, replace output shaft speed sensor, replace automatic transmission, repair engine control module case ground.

So far I have replaced the Mass Air Flow Sensor and the Output Shaft Speed Sensor. I took it to a mechanic and they indicated they found nothing wrong with the spark plugs, ignition coils, or the alternator. It is not miss-firing, and sounds like it is running smooth. The only problems I noticed are that it feels like it is shifting with a lurch when I accelerate from a stop through the second gear, then it shifts fine after that. The other problem is it dies when in drive at a stop (not consistently, but enough that I have to keep an eye on the rpms).

It seemed to be fixed right after I dropped the transmission and replaced the output speed sensor. I'm wondering if that might indicate this is a ground problem.

Any suggestions?

Thanks,
Randy

 

Most likely there is a damaged wire between the PCM and the OSS connector.

Unplug the PCM and the OSS sensor. Probe the BACK of the connector, NEVER push a probe into the end that makes the connection. That spreads the pins and creates open circuits that didn't exist before.

Check each of the two wires to the sensor for continuity from the PCM connector to the OSS sensor. Then check for continuity to ground for each of the wires. Then check for continuity to the power wire for each of the wires.

 

Mark, Thanks! I won't be home till Wednesday, hopefully I will be able to work on it then. I appreciate the advice.

Randy