Bill Slugg Posted January 6 Share Posted January 6 I have a 2008 Fusion, 2.3L, 5 speed automatic. I am getting hard shifting. Code is P-0720, "Speed sensor". I have found there is an input sensor and an output sensor in the transmission. Does anyone know how I can tell which one is the problem? 0 Quote Link to comment Share on other sites More sharing options...
Bill Slugg Posted January 6 Author Share Posted January 6 (edited) https://youtu.be/-2Q4sO1kxKg This guy explains it. The P-0720 code comes from a bad "Revolution Sensor" aka "Output Speed Sensor" aka "OSS", which is on the left of the screen. A P-0500 code (which I do not have) comes from a bad "Vehicle Speed Sensor" aka "VSS" on the right side of the screen. I'm going to take a shot at it. I can't put any substantial amount of money into this car or the wife will pitch a fit and I'd have to buy a new car. It has 150k miles, lots of body damage, transmission already clunks, this problem only made the clunk unlivable. Edited January 6 by Bill Slugg 0 Quote Link to comment Share on other sites More sharing options...
WKelley Posted January 6 Share Posted January 6 You do realize that the P0720 code is likely different between Ford and Nissan, correct? When my 2010 2.5L 6spd manual had issues with the speedo it threw a P0720. Replacing the VSS solved my problem. Do you have any issues with the speedo? 0 Quote Link to comment Share on other sites More sharing options...
Bill Slugg Posted January 6 Author Share Posted January 6 No issues with the speedo. That would be the Vehicle Speed Sensor on the output side of the transmission and would be code P-0500. The Output Speed Sensor, code P-0720, is the output of the engine, not the transmission. However, now I find a source says the P-0720 code can also be generated by a bad VSS as well as the OSS. Also this source also says the code can be generated by low oil level and also defective shifting solenoids. With 150,000 miles and never having had the transmission oil changed, that is a possible cause that should be dealt with first. I plan to get about a dozen quarts of fluid, drain through the plug. Flush through the rubber hose going to the cooler. Flush until brown fluid becomes red. Fill and check level when hot. Evaluate the impact on the hard shifting. Then look at replacing the OSS, since it is east to get to, only requires removing battery tray. If that won't work, I'll look at replacing the VSS, but that requires dropping the exhaust. I have no lift so that will be problematic. 0 Quote Link to comment Share on other sites More sharing options...
Bill Slugg Posted January 7 Author Share Posted January 7 (edited) I started to the store for some fluid and noticed the speedometer at zero. I had never seen this before. When I got to about 40 mph it suddenly shot up and acted normally. I cancelled the fluid run and turned around, it did it several times on the way home. I reached under the battery and pulled the connector off of the Output Speed Sensor. Ran around the block and the speedometer came on intermittently, sometimes at zero, sometimes at correct speed. Had the OSS been at fault I would have expected to see speed at zero all the time, but it wasn't. Conclusions: 1)The problem is not the Output Speed Sensor on the engine, the problem is the Vehicle Speed Sensor on the output of the transmission. 2) On this vehicle, code P-0720 must refer to both sensors. The VSS is very difficult to get to. I will crib the vehicle up about 18", get under there and start planning to drop the exhaust and get to it. If successful, then I will change fluid. Edited January 7 by Bill Slugg 0 Quote Link to comment Share on other sites More sharing options...
WKelley Posted January 7 Share Posted January 7 The garage that fixed mine said there were some history codes in there that also pointed to the VSS. The only active code I had was P0720 though. Good luck! 0 Quote Link to comment Share on other sites More sharing options...
Bill Slugg Posted January 7 Author Share Posted January 7 I have another wrinkle to toss in here. I checked my transmission fluid level with the engine cold and with it at operating temperature. Both checks show the level to be 2" above the high end of the range. I have no idea how this happened. My wife got the car new and I have never so much as checked the level. Only place its ever been serviced is at the dealer. I suspect a bad seal somewhere letting engine oil in but that's just a wild guess. 0 Quote Link to comment Share on other sites More sharing options...
WKelley Posted January 11 Share Posted January 11 It's not physically possible to get engine oil to leak in the transmission. It is possible to get coolant in the transmission if the trans cooler in the rad fails. This would cause the trans fluid to look like strawberry milk and is easy to spot. I think the level is a red herring, fluid level does not effect sensor operation. 0 Quote Link to comment Share on other sites More sharing options...
Bill Slugg Posted January 25 Author Share Posted January 25 (edited) I drained what fluid I could out of the pan plug, got about 4 quarts. It only took 3 quarts to put it on correct level. It was dark brown, not strawberry milky. I changed Output Speed Sensors and it did not clear code P-0720. While changing, I noticed a spot on one wire that might have been broken inside. When I went to pull the plug out so I could better access the potential broken wire, one of the three wires broke clean off, flush with the sensor plug. When I cut the plug out and looked at it, there was a second wire broken inside the insulation but the insulation had not broken yet. I went to three auto parts stores and could not find the correct plug. Comparable plugs were $50 so I figured it would be over $100 at a dealer. Since I had two good sensors, I cut the plastic off one enough to expose the three prongs, soldered leads to each one, soldered into the wires in the harness, fired it up, no codes, speedometer works, shifting is smoother. There is lots of relative movement between the wiring harness and the OSS, 16 years of flexing broke the wires. Should be OK now, thanks for the assistance. Edited January 29 by Bill Slugg 1 Quote Link to comment Share on other sites More sharing options...
Grampy Posted February 12 Share Posted February 12 On 1/25/2024 at 6:59 PM, Bill Slugg said: I cut the plastic off one enough to expose the three prongs, soldered leads to each one, soldered into the wires in the harness, fired it up, no codes, speedometer works, shifting is smoother. There is lots of relative movement between the wiring harness and the OSS, 16 years of flexing broke the wires. Should be OK now, thanks for the assistance. The kind of repair that makes me proud to know there are other people out there that know how things work and /or how to troubleshoot, and don't just take it to a dealer and pay $1000 for what could have been an easy repair. Example, my wife took her '02 Explorer in because 4WD wasn't engaging.. they told her it needed an $800 module + labor.. I had her bring it home so I could look at it after work... I looked at the wiring diagram, crawled underneath \found the ground wire that was broke off of the transfer case. Installed a NEW more robust grounding strap.. worked great for years afterwards, even after we gave it to her brother.. eventually he abused it enough to trash the transmission. 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.