OSS HELP - How do you Diagnose Correctly
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New User
Joined: Mar 2015
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Bringing this thread back from the dead! I have still have not resolved the problem associated with the P0720 code.
What I have done so far:
1. Tested sensor and confirmed it was working.
2. Replaced sensor pigtail.
3. Checked signal return wire and signal feed wire. Both wires have continuity from sensor pigtail to PCM connector.
4. Replaced PCM. Found a used one at a good price and wanted to rule it out.
I still haven't checked the tone ring on the tailshaft. What is the best way to check it? I am assuming it can be done without dropping the tranny. Is the tone ring a common problem? It seems like a metal tone ring would not break very easily. Is there anything I am missing????
I AM ABOUT TO SET FIRE TO THIS TRUCK!!! BEYOND OVER IT.
Any Help would be greatly appreciated.
What I have done so far:
1. Tested sensor and confirmed it was working.
2. Replaced sensor pigtail.
3. Checked signal return wire and signal feed wire. Both wires have continuity from sensor pigtail to PCM connector.
4. Replaced PCM. Found a used one at a good price and wanted to rule it out.
I still haven't checked the tone ring on the tailshaft. What is the best way to check it? I am assuming it can be done without dropping the tranny. Is the tone ring a common problem? It seems like a metal tone ring would not break very easily. Is there anything I am missing????
I AM ABOUT TO SET FIRE TO THIS TRUCK!!! BEYOND OVER IT.
Any Help would be greatly appreciated.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,652
From: SE Florida
How did you test this?
Not a bad thing to do, but was there a reason? Were the pins corroded?
How about continuity to ground or power? If either wire has a short to power or ground it will still have continuity between the connectors, but it will not transmit the signal.
That's really hunting for a solution. A PCM failure is always possible, but it is really, really rare.
I've never seen one fail. You can remove the extension housing on the rear of the trans without dropping the trans. This will expose the tone wheel.
When checking the continuity of the wiring you didn't stick a probe into the end of the connectors that makes the connection, did you? This will open the pins and cause a bad connection where there wasn't one before.
The only other thing I can think of is that there are different length sensors. If you have the wrong one the sensor isn't going to read. The air gap between the sensor and the tone wheel has to be correct.
Not a bad thing to do, but was there a reason? Were the pins corroded?
When checking the continuity of the wiring you didn't stick a probe into the end of the connectors that makes the connection, did you? This will open the pins and cause a bad connection where there wasn't one before.
The only other thing I can think of is that there are different length sensors. If you have the wrong one the sensor isn't going to read. The air gap between the sensor and the tone wheel has to be correct.
Thread Starter
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New User
Joined: Mar 2015
Posts: 10
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How did you test this?
- Pulled and tested the OSS sensor on the rear tail shaft of the tranny. Waved pliers in front of the sensor, with my meter attached and ensured the magnetic properties of the sensor were working properly. Ohmed the sensor out and it was within range at 1.2. Concluded sensor is good.
Not a bad thing to do, but was there a reason? Were the pins corroded?
- Pins were not corroded. One of the tabs on the pigtail was missing. Thought maybe the pigtail might have been wiggling loose and wasn't seated properly to the sensor when driving and bouncing around.
How about continuity to ground or power? If either wire has a short to power or ground it will still have continuity between the connectors, but it will not transmit the signal.
- I didn't check that. Would I just need to find the main power and ground wires to the PCM?
That's really hunting for a solution. A PCM failure is always possible, but it is really, really rare.
- I was so over it, I just decided to give it a try. It was only $100 and I got a newer PCM with better factory programming.
I've never seen one fail. You can remove the extension housing on the rear of the trans without dropping the trans. This will expose the tone wheel.
- I guess this will be a last resort. I have a hard time believing this is the problem.
When checking the continuity of the wiring you didn't stick a probe into the end of the connectors that makes the connection, did you? This will open the pins and cause a bad connection where there wasn't one before.
- No, I didn't I probed from the backside.
The only other thing I can think of is that there are different length sensors. If you have the wrong one the sensor isn't going to read. The air gap between the sensor and the tone wheel has to be correct.
- How would I check that? Pull the sensor and bring it with me to the dealer to compare their sensor to mine?
- Pulled and tested the OSS sensor on the rear tail shaft of the tranny. Waved pliers in front of the sensor, with my meter attached and ensured the magnetic properties of the sensor were working properly. Ohmed the sensor out and it was within range at 1.2. Concluded sensor is good.
Not a bad thing to do, but was there a reason? Were the pins corroded?
- Pins were not corroded. One of the tabs on the pigtail was missing. Thought maybe the pigtail might have been wiggling loose and wasn't seated properly to the sensor when driving and bouncing around.
How about continuity to ground or power? If either wire has a short to power or ground it will still have continuity between the connectors, but it will not transmit the signal.
- I didn't check that. Would I just need to find the main power and ground wires to the PCM?
That's really hunting for a solution. A PCM failure is always possible, but it is really, really rare.
- I was so over it, I just decided to give it a try. It was only $100 and I got a newer PCM with better factory programming.
I've never seen one fail. You can remove the extension housing on the rear of the trans without dropping the trans. This will expose the tone wheel.
- I guess this will be a last resort. I have a hard time believing this is the problem.
When checking the continuity of the wiring you didn't stick a probe into the end of the connectors that makes the connection, did you? This will open the pins and cause a bad connection where there wasn't one before.
- No, I didn't I probed from the backside.
The only other thing I can think of is that there are different length sensors. If you have the wrong one the sensor isn't going to read. The air gap between the sensor and the tone wheel has to be correct.
- How would I check that? Pull the sensor and bring it with me to the dealer to compare their sensor to mine?
Thanks Again for all the help.
Tuned
Joined: Jul 2001
Posts: 439
Likes: 0
From: Erie, Pa
Mark,
I have tested the sensor return wire from the OSS sensor to power, and to ground. I have no resistance to power, but I have 1140 ohms between the wire and ground. Does this sound normal, or am I looking at a short to ground?
Steve S.
To many to list.
I have tested the sensor return wire from the OSS sensor to power, and to ground. I have no resistance to power, but I have 1140 ohms between the wire and ground. Does this sound normal, or am I looking at a short to ground?
Steve S.
To many to list.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,652
From: SE Florida
If you had the harness unplugged at both ends that indicates both a short to power and short to ground. If you had it plugged in at one or both ends, the reading is meaningless.
It should have infinite resistance to power and to ground, otherwise known as an open circuit.
It should have infinite resistance to power and to ground, otherwise known as an open circuit.
Tuned
Joined: Jul 2001
Posts: 439
Likes: 0
From: Erie, Pa
If you had the harness unplugged at both ends that indicates both a short to power and short to ground. If you had it plugged in at one or both ends, the reading is meaningless.
It should have infinite resistance to power and to ground, otherwise known as an open circuit.
It should have infinite resistance to power and to ground, otherwise known as an open circuit.
Steve S.
To many to list.
Senior User
Joined: Nov 2007
Posts: 128
Likes: 0
From: Kalamazoo, Michigan
There is another sensor in the differential called VCC. It's at the top of the case, mine went bad and cruise failed. Replaced that and no more problems, not sure if that would effect your situation, just might take a look at it. HTH's Lee
New User
Joined: Apr 2020
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Sorry to bring this back from the dead but has anyone fixed this? I have has this problem 5 months ago, tried to diagnose it 3 moths ago and blew the trans trying to figure it out. Well long story short. I put a rebuild in and I'm getting the exact same problems to night. Haven't even drove it. It's just on jack stands right now.
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1st Gear
Joined: Aug 2024
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Alternator was my issue
Sorry to bring this back from the dead but has anyone fixed this? I have has this problem 5 months ago, tried to diagnose it 3 moths ago and blew the trans trying to figure it out. Well long story short. I put a rebuild in and I'm getting the exact same problems to night. Haven't even drove it. It's just on jack stands right now.
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