P0720 Code, O/D Off Flashing. Shifting issues

[Slicer89]

This is for my 2000, V8 AWD XLT Explorer. Automatic. 163kmiles.

A while back my OD off light started to flash and would shift funny between 1st and 2nd gear, but operate fine otherwise, And I was still able to turn overdrive off with the button... I finally got my CEL on and ran it to the nearest parts store to get the codes. It turned out to be the Output speed sensor... Well, After that I would only have my CEL light on but the OD Off light would not flash and it would shift fine.. Then all of the sudden it started shifting really bad, It would take forever to shift into 2nd.. Then it would go into 3rd, back to 2nd then back to 3rd. I finally got around to replacing the OSS and it drove fine for about... 5-8 miles and the OD off light started flashing again, but didn't shift funny. Then I took it to another town about 30 miles away, the light started flashing again, CEL came on and started shifting bad again. I took it to the nearest parts store AGAIN, to find out it was the P0720 code again. "Output speed sensor insufficient input from Output Shaft speed sensor" ( From O'Reilly autparts)

So I am at a loss, I replaced the OSS (O'riellys site called it a transmission speed sensor on their site???) and reset the computer, and it still did as mentioned above.

Says possible causes:

OSS Connected is damaged (Check pins for damage and for moisture)
OSS Has failed (IT may be damaged)
OSS Signal circuit is open, shorted to ground or shorted to voltage
PCM has failed (I really hope this isn't the case)

What else there for me to do? Whenever I reset the CEL and what not, it shifts PERFECT! No shudder, hesitation, skipping or anything. Shifts buttery smooth. the fluid is cherry red and doesn't smell or appear burnt.

Can anyone help me figure this out? Is there more than one OSS? Is it possible I got a bad OSS? Is it possible that I just need to clean the hole the sensor goes into?

 

[Samb148]

It sounds like the gear that turns your speed sensor is junk. I had an f150 that did the same thing.

 

[Slicer89]

It sounds like the gear that turns your speed sensor is junk. I had an f150 that did the same thing.

Is this something I can replace on my own? Or does it require pulling the transmission out?

I really hope that isn't the issue...

Thing is, The sensor itself doesn't appear to have anything on it that spins. So I'm not sure what the issue would be.

I hope someone else can chime in and shed a little light on the situation, Because if my OSS gear thing is shot... The whole damn transmission will need to be pulled won't it

 

[Samb148]

In not sure if it would or not on yours. They are two different transnissions. I just know mine had a plastic gear that went in the tail of the tranny. I'm not sure what yours is like. The inky other things I can think if are checking the wiring down to the sensor and having your pcm checked or flashed.

 

[Slicer89]

In not sure if it would or not on yours. They are two different transnissions. I just know mine had a plastic gear that went in the tail of the tranny. I'm not sure what yours is like. The inky other things I can think if are checking the wiring down to the sensor and having your pcm checked or flashed.

The OSS on this tranny (5R55E I believe) is on the top middle near the range sensor (I think?) and doesn't appear to have any mechanical parts on the sensor itself.

How would I get my PCM checked or flashed? Someone told me if the PCM failed it would not move at all.

 

[Samb148]

If it is pcm, I know a dealer can flash it but rock auto has them for my 2000 sport for around $160 if I remember correctly. I'm not sure if a private mechanic could flash it or not. I would guess it depends on their equipment. I had a bad pcm in a Chrysler once and it still ran.it just made the cel stay on

 

[Slicer89]

If it is pcm, I know a dealer can flash it but rock auto has them for my 2000 sport for around $160 if I remember correctly. I'm not sure if a private mechanic could flash it or not. I would guess it depends on their equipment. I had a bad pcm in a Chrysler once and it still ran.it just made the cel stay on

Are there any other symptoms to a bad PCM? I'm really hoping that isn't the issue...

I could use more input on this. I'm sure someone else out there might have any idea.

 

[Slicer89]

anyone else? Had some one look at yesterday, And they claim because "My chain is slipping teeth in the Transfer case, it's throwing the "timing" off everything throwing a code and causing it to shift funny and what not"

Then my father talked to someone who said that the torque converter might be screwing up as well.

I'm at a loss, I love this vehicle but don't know what to do.

 

[JK080]

I don't think anything is wrong with the transmission itself.

Its sounds like you are just losing the OSS sensor signal, if you have already replaced the sensor I would think it could be the connector or wiring. A scanner that can read the data stream can help catch the glitch and you can use it to find the failure by moving and pulling on the wire harness and connector while watching the scan tool for the drop in signal. Obviously it would help to have a lift it being a AWD but maybe you have a option for neutral on the transfer case, not sure about that.

 

[Slicer89]

I don't think anything is wrong with the transmission itself.

Its sounds like you are just losing the OSS sensor signal, if you have already replaced the sensor I would think it could be the connector or wiring. A scanner that can read the data stream can help catch the glitch and you can use it to find the failure by moving and pulling on the wire harness and connector while watching the scan tool for the drop in signal. Obviously it would help to have a lift it being a AWD but maybe you have a option for neutral on the transfer case, not sure about that.

I didn't think it was the transmission itself, Because it shifts perfectly fine until the O/D off light starts to flash / And the CEL comes on.

Is there anything else I can check? A fuse? Maybe clean the connector, And clean the hole the sensor goes into?

 

[JK080]

It wont be a fuse, they stay blown and cleaning the sensor hole wont change anything. The trick is to be able to monitor the connection, you need to know when the connection is lost to find the weak spot. Ohm reading on the wire from end to end with a basic DVM might show something but it would be some work.

Sure check all connections even the one at the ECM, and look for chafing on harness looms and insulation from the tranny to the ECM, other than that its going to be tough without the proper tools.

 

[Slicer89]

It wont be a fuse, they stay blown and cleaning the sensor hole wont change anything. The trick is to be able to monitor the connection, you need to know when the connection is lost to find the weak spot. Ohm reading on the wire from end to end with a basic DVM might show something but it would be some work.

Sure check all connections even the one at the ECM, and look for chafing on harness looms and insulation from the tranny to the ECM, other than that its going to be tough without the proper tools.

True, That is very true. On the fuse part atleast.

I don't really have any way to monitor, There is a shop locally that could do diagnostics, but not sure how extensive they could do it.

 

[Slicer89]

Going to bump this.

What connections should I check and clean? Any fuses? Under the hood? I'm gonna buy some electrical contact cleaner and clean some of the wire lumes under the vehicle and on the transmission, gonna check all the connections I can under the hood as well.

What about the range sensor? Would that cause any issues? Even if it's throwing the P0720 code...

What else can I test / clean?

 

[Slicer89]

Going to bump again... An hour of Google searching didn't really help me at all, it didn't really lead to anything that would help me.

The local shop wants to charge me $80 for a diagnostic, and then $98/hour to try to track down the problem, They apparently won't just do a diagnostic and let me do the rest. So I have to try to figure this out myself.

 

[Slicer89]

One last bump before I decide to sell it as scrap.. The local shop wants WAY too much to diagnose it. Can't even talk the guy into just putting on a diagnoses....

So, If theres anymore input, PLEASE post. I'm gonna go out later this week and start blasting connections with contact cleaner, Try resetting the PCM and cleaning up other connections, checking them and checking the sensor itself.

 

[JK080]

This is all I got hope this helps.

1. Unplug the Output Shaft Speed (OSS) sensor and check the resistance of the sensor, specs are 305-735 ohms of resistance. Replace the sensor if it fails the resistance test.

2. If OK, install an AC voltmeter on the two pins and check the AC output as the drive wheels are turning. The greater the speed, the higher the output. Replace the sensor if there is no AC voltage generated.

3. If OK, check for an open or shorted wire on the Dark Blue/Yellow (DB/YE) wire that goes to pin 84 of the PCM.

4. If OK, check the Gray/Red (GY/RD) wire that goes to pin 91 of the PCM for shorts or opens.

 

[Slicer89]

O/d Off flashing, P0720 & P0721 codes

I've posted this before about the OD off light flashing in my 2000 V8 AWD explorer, It's still doing it even after replacing the sensor. I checked and cleaned all connections and reset the PCM, Still the same thing.

Whenever the OD off flashes, it starts to shift rather... illradically. But before the light flashes, it's fine.

RPMS are less than 2500 at 70mph. Cruise works, doesn't shudder or slip. Doesn't feel like it is anyways

I finally took it to a place that has a good OBD2 scanner, It scanned the power train and all it found was

P0720 Output speed sensor fault
P0721 - Output speed sensor performance

That's all it had. The guy cleared the codes, and it still started flashing and giving me trouble.


Any ideas? Likely I got sold a bad, or improper sensor? All the connections look fine, I cleaned them with contact cleaner and checked what I could see of the loom.

What else would cause this?

 

[Slicer89]

It also now has a P1000 code. Because the guy reset or cleared all the trouble codes. Now I don't know what to do to reset it. Someone posted a how to, but I do not have unlimited access to a scan tool.

 

[drdoom]

Replace the sensor that should take care of it.

 

[Turdle]

I merged the 2 threads so folks will not make redundant suggestions.