slowstang06

Hey all, I just bought a 2000 GT, shortly after my test drive and after I bought the car I was driving and when I was coasting in neutral I saw the speedo shoot up to 50-80mph and come back down, it did this a couple of times.

Then while driving my buddy behind me called me to tell me to slow down since it was a 45 zone, and I looked at my speedo and it was right under 45 and he was going about 60 to keep page with me, same for on the interstate it was about 15 mph off (depending on if I was in 4th or 5th). When I got home I used my old SCT scanner from my old '06 GT and it gave me a code ,P0721, what should I do to fix it? The old owner said he put 3.73s in it about 6 months ago but that it wasn't that off for him?

I searched the code and got: P0721: Output Shaft Speed Sensor circuit. How would I locate the wiring for it/where is it at to check?

EDIT: Here is a video of the car doing its thing a little bit View My Video . (excuse Gucci Mane, CD came with the car, so I'm working on my street cred a little bit) It was going haywire this morning jumping all around. I did the gauge trick to see what DTC came up that way and it was D262. I noticed the RPMs seem to hang a little bit (previous owner had ford replace the IAC though) too.

I checked the OSS and it looked fine still to me, should I go ahead and replace?

rednekpimp

congrats on your new purchase. If i'm not mistaken, the speed sensor is located on trans., driver side towards the rear. I believe it is has a two pin harness plugged in to it. most can be puirchased at any part store for under $20.

slowstang06

thank you! I went and found it, and I didn't replace it, just inspected it and cleared the code, I want to drive around a little bit and see if it comes back on.

slowstang06

Bump for any more opinions after getting a video up..

Here is a video of the car doing its thing a little bit View My Video . (excuse Gucci Mane, CD came with the car, so I'm working on my street cred a little bit) It was going haywire this morning jumping all around. I did the gauge trick to see what DTC came up that way and it was D262. I noticed the RPMs seem to hang a little bit (previous owner had ford replace the IAC though) too.

I checked the OSS and it looked fine still to me, should I go ahead and replace?

cliffyk

The speedometer (and odometer, tachometer and coolant temperature gauges) are controlled by a microcontroller in the instrument cluster, based on values received as digital data packets via the Standard Corporate Protocol (SCP), the J1850 OBD2 data stream. The code D262 means there was a missing SCP message--more about the cluster diagnostic mode here.

This could be the result of a wiring problem (a bad ground would be my first suspicion) in the SCP bus between the PCM and the cluster, or a bad cluster or possibly PCM.

It could maybe be a bad OSS sensor, I do not know to what extent the PCM monitors and validates the timing of individual pulses in the OSS sensor output...

slowstang06

Thank you for that! Would you recommend me just pulling the cluster out and checking the wiring or taking it to Ford?

cliffyk

Does your SCT scanner allow data-logging of vehicle speed? If so then I would first use it to monitor same and see if it reads consistently, or mimics the behaviour of the speedometer. If the data-logged speed is not affected then you will know it's a problem with either the wiring between the DLC (Data Link Connector, the OBD2 port) and the instrument cluster or the cluster itself. If that is the case then pull the cluster and check the connectors and wiring (you'll need to unplug the connectors to remove the cluster).

Make sure the connector to the OSS sensor is clean and properly plugged in (unplug it and visually insect the male and female connector bodies), and that the wiring it not damaged.

The OSS sensor can be checked with an ohmmeter, resistance between the pins d should be 450Ω to 750Ω...


A couple of other thoughts:

With 3.73 gears, and nothing done to correct the speedometer, the speedometer should read faster than actual speed by +14%. This can be corrected in one of two ways; by modifying the tune, or using a VSS pulse scaling device such as the Dallas SpeedCal.

Which leads to my second thought. If someone installed a SpeedCal or similar device, and it's wiring has been compromised then it could perhaps create the problems your are experiencing. Such devices are usually installed at or near the shift turret, it might be worth pulling the shift bezel just to take a look.

slowstang06

I'm not sure about the SCT, it's an X3 but I'll try it out this weekend... I bought an SCT chip with a tune for the tire size and the gears, but if they tried to do something and it's messing up both? Today it was particularly bad, it told me I drove a mile while I was sitting at a stop light http://i87.photobucket.com/albums/k1...4FA9C4F6FE.mp4

slowstang06

So, I data logged the car and the scanner read the same speed as the speedometer, even when the needle would jump around twitch. I had hopped it would have read correctly because then the previous code for the SCP would have made sense. Also, the P0721 code is back... The car has been tuned now for the 3.73s it just hasn't made any difference.

cliffyk

If you are still running the "chip" make sure the J3 connector on the PCM is clean and bright--scrubbing off the protective coating can take some diligence and if any pin has a bad connection it can cause problems...