Cadillac PCO717 code
I had a PC0717 error in the PCM section of the diagnostic codes. My research a few years ago led me to the following page.
I found a direct correlation between sensor failure and the temperature of the engine. I tested this by clearing the codes before going to bed and then seeing how long it took before the code happened again. The code would take longer to trip during the winter and it happened faster in summer. The page above refers to heat affecting the sensor. This error occurs because of the failure of the reluctance pickup on the input shaft to the transmission. A reluctance pickup is simply a coil of wire encased in epoxy resin whose job is to count the revolutions of a spinning shaft. There are other purposes for pickups, but this is the purpose of the one in question. When reluctance pickups begin to fail, they become much more sensitive to heat. Why you ask? It's because that epoxy case gets a crack in it and the wire cracks right along with it. When the case is cool, it contracts and the broken ends of the wire touch and it does its job. When it heats up, the case expands and the broken ends of the wire separate. When those wires don't touch, the pickup cannot work.
Clinical diagnosis is done by measuring the resistance across the two leads going to this reluctance pickup. The measurement must be done when the symptom is active. It other words, that engine must be hot. If you want an accurate diagnosis, make an appointment at a GM dealer that is familar with Cadillacs. Ask questions, make sure the technician knows his stuff and is familiar with this particular problem. I was fortunate to have a VERY good tech. If you're close to Grand Forks, ND, I highly recommend Shannon at Rydell Auto Center. Take this post with you and have him read it. Clear your codes on the morning of the appointment. Drive the car until the 0717 error occurs. Drive directly to the dealer and have him do a resistance check of the pickup.
This sensor is deep in the transmission. Although the link above says this repair can be done with the transmission in the car, my tech said it was not possible.
I drove my car for two years with this problem. There were times when the shifting seemed a little harsh, but it wasn't alarming. I feel I lost 15% in fuel efficency because of this problem. I believe the reduction in gas mileage happens because there is a loss in transmission efficiency when the error is present. I remember reading something about the transmission going into some sort of reduced operational mode when the code trips. This might happen to prevent serious damage. Depending on the miles you put on the car and how long you plan on keeping it, you may find that the repair cost is mitigated by the increase in gas mileage. I averaged 19.8 mpg before the repair and 22.8 after.
If you're comfortable with heavy duty car repair and have time, you might be able to follow the steps in the link above. Otherwise have a reputable GM shop repair the car. DON'T install a used transmission. Why? Because this failure is common and you don't want to pay for the installation of another faulty transmission. I've heard of this happening. Don't go to a generic transmission shop. If you want a good fix, then go to a GM tech who has experience with these units.
If you decide to have the unit repaired, there is another common transmission failure that should be tended to while they have the unit out. There's a shaft in there that transfers pressurized transmission fluid. It's purpose is to lockup the torque converter. There are seals in that shaft that get old and begin to leak. If the leak is severe enough, the torque won't lock completely and the clutch plates will burn up.
The "optional" repairs mentioned in the above link are good ideas. I had the front bearing in my A/C compressor replaced, the transmission sensor mentioned above replaced, seals in that shaft done, a filter inside the transmission replaced, the pass through wiring harness to the transmission was replaced. There were a couple other things replaced in the transmission that I can't remember, they weren't too significant though. I also had some hard starting problems and they replaced an O2 sensor and my fuel pressure regulator. I had them fix the famous oil leak, which was cost a bit too. They replaced my heater hoses. The aligned the front end due to the removal the transmission.
My caddy has 162k on it and it looks wonderful. I love the car and hope to keep it for quite a while. I bought it in 2000 with 80k on it. I figure if I get another 2 to 3 years of use out of it, the repair was worth it. My latest project on the car is a new audio deck, speakers and woofer. Can't wait.
The following link will show you my invoice for everything done. I hope it helps you.
Keep in mind that your transmission parts cost will be higher. I had originally intended to do the repair myself and bought most of the necessary parts two years ago. There were several other seals and odds and ends they needed and those are shown in the above invoice. Check out the parts prices at http://gmpartsdirect.com.