Hello Ford friends. I need a little advice, or even some straight answers if you've got them.

I picked up a project truck, 1995, 302, 4R70W 2wd. All is great except for the fact that I've got a continuous code / running code 639 - Insufficient Input from Turbine Speed Sensor/Ouput Shaft Speed Sensor/Transmission Speed Sensor - apparently this sensor has many names but we're talking about the one on the Transmission, not the differential. Symptoms are crappy/erratic shifting, blinking OD light after 1st gear shifts. Then blinking in 2nd gear. Lower than 10mph no blinking. Speedometer module had blown up at some point. I replaced that, so at least I have a speedo now...

First thing I checked was the fuses. They’re good. I bought a new OSS/TSS sensor just to have on hand in the event that I got lucky and it was actually the sensor but I don't think that's where I'm at anymore. I checked the resistance of the sensor and it is within spec at 4 degrees F (459 ohms). I haven't been able to visually inspect the rest of the sensor because that thing is stuck in the transmission like you wouldn't believe. I'm guessing that it's stuck because of the cold - it was 4 degrees last night during attempt #1 or the age, or, a combination of both. This sensor has a Ford logo on it so I'm assuming it is original and has gotten attached to its home of 19 years.

The only concerning thing I've found so far is that the clips for the harness are broken off on both sides and it appears that there was some oil leaking onto the harness at one point. I cleaned the harness and inspected the pins as well as I could and they appear to be corrosion free. This also leads me to believe that the previous owner had tried to deal with this or that the transmission had been out of the truck at some point. Either way, someone removed the harness at some point and broke the clips. It's wiggly. Doesn't seat well. Once I get the new sensor in I'm going to zip tie it and hopefully that helps with the wiggle. I haven’t done a ‘wiggle test’ as I am doing this alone and it seems that the wiggle test might require 2 people and I also don’t know if I can do a wiggle test on this since it gets info when the truck is moving.

Anyway, I have searched around for some information on this subject but I've come up with limited information except for a diesel truck website which outlines the Ford procedure for testing. The Ford procedure involves using a breakout box. I don't have a breakout box and I'd like to at least try to test the circuit to make sure that there's no short or that there's supply to the sensor (if that's how this circuit works).

Is there a procedure to test without a breakout box aside from checking the resistance of the sensor? Is any current being supplied to that sensor? Is there a voltage to or from the sensor with the key in the RUN position?

Back to the sensor not budging: It rotates, but doesn’t come out. Would heating the area around that the sensor be a safe thing to do in order to try to wiggle it out? I mean, this thing is stuck badly. Normally I wouldn’t talk blow torch for a sensor but I don’t believe how stuck this thing is. If the sensor wasn't messed up yesterday, it sure is now - yanked at it with pliers, tried to lever it out with a screwdriver - so it needs to come out. Everyone says "it'll just pop right out" but that definitely isn't happening – and yes – I removed the 5/16" bolt from the retaining clip. I'm thinking about torching or heating (with heat gun) the case a little around the location of the sensor. If it doesn't budge, I'm thinking about torching it more to the point that those o rings might start to melt. Is there anything that I can potentially destroy in that process besides the sensor? I'm just concerned about what's inside the case, really. I'm not too familiar with the 4R70W or AODE transmissions and I’m worried about melting something internally. I had one on my Crown Victoria but I never had to do anything more than change the fluid and filter.

Steve83, who has indirectly provided me - and probably all of us - with tons of useful info in the past, has a lot of info on the PSOM and other components but before I go down a rabbit hole and start testing those things, I’d like to see if I can get past this sensor/circuit first.

Thanks for reading. Hope this is clear. Any advice is welcome.

Thanks,
Mike

 

A bad PSOM is not going to trigger Code 639. I would not go down that path until you resolve that code issue. The OSS is a vital input to the PCM. A lack of or incorrect value will cause shifting issues.

I would suggest you trace the signal wire integrity from the OSS/TSS to the computer (PCM) on Pin 5 and 29.

As far as getting the old one out....everything I read also states it should just "pop out". Perhaps a bigger hammer and few more adult beverages are in your future.

 

Good evening. Thanks for that. I wasn't sure if that sensor was tied into the PSOM so thank you for clearing that up.

I went out this afternoon after work and tried to get the sensor out again. Torched the hell out of the case. Sensor snapped. My last resort I guess is to heat an ice pick until it's glowing and slowly work it around the plastic to free those o rings. I don't want to damage the aluminum so I'd rather melt it than scrape it away. If that doesn't work I guess I'll have to knock it out from the inside. We use a lot of road salt here and I see the white scale around the plastic so my guess is that there's a nice ring of salt and crud and scale holding that sensor in.

Once I get the stupid thing out I'll secure that harness and then check those terminals. It's 4 degrees tonight... I have the adult beverage part covered but the truck can wait. The next warm day is Saturday. It will be 33.

 

You have a "O" ring problem. The "O" ring is stuck to the Transmission OSS hole.
This problem happens with the distributor as well and makes them very hard to get out.

The Brake-Out-Box (BOB) pin numbers are the same as the PCM Computer plug pins as that is what you plug into the BOB. So you can back probe those wires or unplug the PCM Computer to test circuit better.

The output shaft speed sensor (OSS) is a magnetic pickup, located at the output shaft ring gear that sends a signal to the powertrain control module to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, shift scheduling, determining EPC pressure.

To test OSS sensor connect an ohmmeter between the negative lead to +OSS and positive lead to -OSS.
Resistance should be between 450 and 750 ohms from pin 46 to pin 5.


/

 

Thanks for the help with the circuit info. Much appreciated.

I talked to a friend of mine who is a mechanical engineer in the Navy and he told me to use either vinegar or ammonia to loosen up the aluminum oxide around that o-ring. Incidentally, something I never knew, was that aluminum is so corrosion resistant because of the layer of aluminum oxide that forms on the surface when it contacts the atmosphere.

Anyway, ammonia and a hard bristled tooth brush removed that junk pretty quickly. I went around the sensor with a pick for good measure and then forced the remainder of the sensor out with a vise grip.

When I took the sensor out, it looked very different than the one I was installing. I think the previous owner used one from a later 4R70W or just the complete wrong sensor. It also had little magnetic ability left in it.

I installed the new one, checked the circuit, cleared the trouble codes and so far have put 35 miles on the truck and no OD flash. Going to put another 40 or so on it today and hope that's that.

I'm not surprised if the previous owner put the wrong sensor in. Based on the condition of the air filter (the first thing I changed), this truck had been suffering! There's nothing I hate more than poor vehicle maintenance.

Thanks again for the help.

-Mike

 

Also, Subford, breakout box looks might nice to have. Thinking about buying one.

The reason I was hesitant to back probe the connector is because of so many things I've read about damaging it that way. The probes on my fluke are pretty fat and I didn't wanna go sticking pins in there.

I'm guessing you can probably verify that back probing the ECU harness it is harmless if done with care?

 

Yes they are nice.
I use mine a lot. I just wish it was easier to get the plug off the PCM Computer as that would make it a lot faster to plug the BOB into it.

The sensor recorder is nice too when you drive also but do not use it much. But it comes in handy when I want to look at the MAP sensor but it will recode any sensor for looking at some time later. I mostly only use it if the truck dose not have the data out put at the self-test plug for my scanner.