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Code PCO717 1996 Cadillac Seville STS
    By Ray Greulich

Question mark

Ok, so you got the dreaded code PC0717. What is it, and how do you fix it?

First off it is a speed sensor that tells your cars computer how fast the transmission input shaft is turning. Without this information my car did not know when to shift, and when it did shift it was very harsh. Can you drive your car with this code present? Yes you can, for how long your transmission will last like this I don’t know. Mine shifted so harsh that I was afraid to drive it very much.

Some of the generic transmission manuals call this sensor a “turbine speed sensor”. On the 4T80E transmission it is mounted next to a gear that comes off the input shaft, which is behind the torque converter. I assume that the “turbine” the manuals refer to is the torque converter. I was quoted 12+ hours labor plus parts by the local GM dealer to change the sensor. The service manager quoted around $1200.00 for the complete job. I decided to tackle the job myself. But first I had to ask myself is this, why is the code present?  Is it really the sensor? If it is the sensor, is it worth doing all this work just to change the sensor when my car has 148,000 miles? I guess the real question is “should I just let a shop rebuild the transmission and change the sensor”.

First there are some checks in the service manual that check the wiring from the computer to the sensor. There is a resistance value that the sensor is supposed to have, or it is bad. My car only set the code when it was hot. When the car was cold the check engine light was out. I did not do the wiring check, I just checked my wiring visually very carefully from the transmission to the computer, and could not find any damage. Since the sensors are known to be faulty on these cars I made the call that the sensor was the problem. As far as the transmissions mechanical shape goes, I felt that is was OK even though it had high miles. The fluid had been changed on a regular basis, and it was operating very smoothly before the code started to appear. Once I removed the sensor I put an ohm meter on it to check the sensor, and since the car was cold, the sensor read like it was OK. Once I changed the sensor, the code has not set since then. This leads me to question how valid doing a resistance check is.

Can you do the job yourself? I would say that if you just own a basic set of tools and just do things like change your oil and plugs, you should probably stay away from it, if you are not afraid to tackle an engine overhaul yourself I would say that you should be able to do this job as well.

  The speed sensor can be changed without removing the transmission from the car. The engine/transmission can be lowered to access the transmission side covers and the end plate. It is located inside the transmission. The sensor is located next to the sprocket for the input shaft. The sensor is held in place with 2 6mm bolts, one for the sensor, one for the wiring harness.

  If you decide to try this job yourself I would recommend going to a transmission rebuild shop, or look on the Net for an overhaul manual for this transmission, they are about US$15.00. These will give torques, diagrams and assembly practices for this transmission. The manual will not cover just removing and replacing the sensor, it covers a complete overhaul. That is why I built this how-to section, it will give you an idea where it is at, and save you some time.

  Before getting started I recommend cleaning the engine externally. Once the side covers are off the transmission it is easy to knock debris into the transmission while working in the wheel well.

 The first thing that needs to be done is to put the car on jack stands. Jack the car up, and put the jack stands under the body frame, just behind the engine cradle. If you support the car on the engine frame you will not be able to lower the engine!

 You will either have to remove the hood, or disconnect the hood strut rods to allow the hood to be opened farther than it normally does. I disconnected the strut rods, and raised the hood carefully, and then tied off the hood to the A frame that I used to lower the engine. This allows for clearance between your hoist and the hood. Now is a good time to disconnect the battery.

 The engine has to be lowered, you can use an “A” frame, cherry picker or overhead hoist. The overhead type hoists allow for easy access to the engine compartment while the engine is lowered and the hoist remains out of the way.

 The next thing to do is remove the left hand suspension strut. First remove the left wheel and the two plastic panels from the inside of the wheel well. Then I disconnected my strut at the lower ball joint, and disconnected the tie rod end. Remove the brake caliper, and wire it up so that it is not hanging on the hose. After you remove the strut completely from the wheel well you will need to wire the caliper all the way up into the top of the strut tower in order to get it out of the way. You will have to disconnect all the wires for the strut. The connector is at the forward end of the wheel well. Then remove the brake hoses from the strut. Next pop the half shaft out of the transmission. The easy way to do this is to buy a nail removal bar like you use to remove shingles from your house, the flat type that is in the shape of an “L”. Place the short end of the bar behind the CV joint, next to the trans case, put the bend of the bar on top of a transmission case bolt head, then strike the opposite end of the bar with a hammer. The CV joint should pop as the “C” clip pops out of its groove inside the transmission. Pull the bottom of the strut away from the car, make sure that you do not pull the inner CV joint out of the case by pulling on the strut, put your hand on the inner part of the inner CV joint, and pull it out of the case with your hand as you pull the strut away from the car. If you pull from the strut you will pop the joint apart, and you will have to remove the CV joint boot to put it back together. (The inner CV joint will pop apart inside the boot, the outer one will not pop apart, as they are different types) Next remove the support bar that runs between the shock towers, mark around the remaining nuts on top of the strut tower that hold the strut to the tower with a magic marker. When you put the strut back in you will be able to put it back where it was and you will not have to align the car if you mark their position. Then remove the remaining nuts from the top of the strut while someone holds the strut, it should drop out of the wheel well now. Warning it is heavy!

 Now you have to lower the engine, but first you should disconnect some wires and things before you lower it or they will get damaged. The engine will have to be lowered more on the left side of the vehicle. Disconnect the following:

 1. Pull up the boot around the joint for the steering rack connection. Remove, not just loosen the bolt that holds the universal joint to the top of the steering rack. It should pull apart as the engine is lowered.

2. Loosen the clamp from the air filter box tube from the engine, remove the wire connector from the air filter box, remove the box from the vehicle.

3. Disconnect the wire connectors from the temp sensors on the AC high side line that runs across the top of the firewall.

4. Remove the plastic shroud from the relay box on the left side of the strut tower.

5. Remove the heavy red wire that enters the relay box from below. It is a 10 mm bolt.

6. Remove the engine computer from its mount. It is underneath the air filter box housed in a plastic shroud. It simply lifts up to be removed, it and is probably stuck on its pins pretty good. Then put the computer on top of the engine. You may have to unbolt the “L” shaped fender support just above the computer.

7. Remove the two connectors from the transmission selector switch at the top of the transmission, aft side of the engine compartment.

8. Take a look around and disconnect any remaining wire connectors that go from the engine to the body on the left side.

9. Remove both upper and lower radiator hoses.

10. Double check that everything else either has enough slack to allow for some movement, or disconnect it!

 The next step is to loosen the bottom pan of the transmission to drain the transmission fluid out.

Now you should be ready to lower the engine. Run a chain from the front engine hoist point to the aft lift point on the left side of the engine. Attach your hoist to the chain and tension it up. Place a floor jack under the right side of the engine frame. Now you can remove the engine cradle bolts, three on each side. Start to lower the engine making sure that you are not pulling any wires as you lower it. You will need to lower the right side as well, but the left side needs to go low enough to be able to remove the transmission side pan. I recommend lowering the engine a couple of inches, then stop to check you are not pulling on any wires or hoses. Then let the engine down another couple inches. Repeat this until the side pan is visible. Once it is down low enough it is time to open up the transmission.

 You will need to mark, or make a map of the position of how all the wire clamps and studs, and bolt positions go for reassembly. Remove the bolts from the side pan. A drain pan will be required as fluid will run out as it is loosened up. The engine frame attaches to the side pan through a mount, the frame will need to be supported when you remove the mount bolts, once the bolts are out of the transmission side pan you can let the frame drop away from the transmission, it will not go too far. This will give you clearance to remove the bottom row of bolts from the pan. Now you may have to slightly bend the anti-lock brake lines up and out of the way to get clearance to remove the side pan. Once the side pan is removed you will be looking at the upper valve body, and the transmission oil pump housing. The oil pump housing sticks out the most. Remove the bolts from the pump housing, remove the oil pump, and the oil pump drive shaft. Once the oil pump is removed the remaining parts should look like this:



There are now two remaining housings in the transmission, The upper valve body to the right, the oil pump body to the left ( the oil pump housing is gone, you already removed it) you do not need to remove them completely, they will come off with the transmission end plate if you follow these instructions. Disconnect the wires from the solenoids and the sensor on the right side. Some of the bolts that hold the pump housing, and upper valve body on have to be removed, most don’t however. The next step is to remove the bolts as shown in the next picture. These bolts pass through the end plate and enter into the transmission itself. The remaining bolts hold the pump housing and upper valve body to the end plate only, and you want to leave them alone.


 Now remove the remaining bolts that go around the end plate that are outside the transmission side pan, again, remember all the positions for the clamps, studs, and bolts. The end plate should be ready to come off now. You will have to pry a little bit to get it to come off, you should not have to pry very hard. IF YOU ARE PRYING WITH A BIG PRY BAR AND THE PLATE IS NOT MOVING THERE IS STILL A BOLT HOLDING THE PLATE ON! Find it, and remove it, the end plated is not glued down, it should come off pretty easy. After the end plate is removed your transmission should look like this:


And the next picture is a close up of the sensor.



The sensor and wiring harness have a wire connector at the top of the transmission. You will need to fish the wires into the same spot the old ones were at. After you install and torque the sensor and wire harness you will need to check the air gap between the sensor and the gear. This information will be found in the transmission manual you should buy.

 Reassembly of the transmission is just opposite what you have just done, with a couple of things to keep in mind.

   The end plate has two gaskets, one that goes around the perimeter of the case, and one small one that goes next to the speed sensor in the middle of the end plate, with no way to hold it as you install the end plate. You will need some kind of media to hold that gasket in place while reinstalling the end plate. Do not use grease to hold the gasket in place, the bearing type greases are high temp and will not melt into the hot transmission fluid and will wind up on your clutch plates! NOT GOOD. Use either assembly lube, or I used Vaseline. I would purchase new transmission case gaskets, they are pretty much available through GM only. The sensor is also a dealer only item.

 The only other caution I can give you is that if you decide to remove the upper valve body, there are two check balls that will fall out when you take the upper valve body off the end plate. The manual for this transmission will show you where they go on reassembly if you have taken that apart, even though there is not any need to. Then you should buy new new gaskets for that as well.

 There is the main transmission filter that plugs into the bottom of the upper valve body, I would change that as well, since you have to remove side cover to change it, now is the time!! It is not shown in any of my pictures.

  The next thing I would recommend you do is not transmission related, but now is the time to do it. Since you have the engine lowered, and the right side of the engine is pulled away from the body, and the hood is either gone or raised higher than normal, change the heater core to engine hoses!!!!! Now is the time, and by the way no time like the present to change the engine coolant, and put in new pellets!

 After the engine and transmission has been reinstalled you will need to fill the transmission, it will take almost 12 quarts!

 Good luck.

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