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Pressure Control Solenoid
12-25-2006, 04:18 AM
I just got a P0742 code from my 2000 Buick LeSabre (116k) the other night after a cross country trip. I can feel the powertrain sort of surging while im in cruise control and I don't seem to have any overdrive. The failure occured very suddenly and doesn't seem to be intermittant. My assumption is that the pressure control solenoid has failed but I am wondering if anyone has actually done that repair successfully on their own. One way or another I am going to fix this problem myself, its just a question of how to approach it given that I don't have the luxury of a tech 2 scan tool for diagnostic purposes. It's hard to know exactly what is causing the TCC circuit to be stuck on when I can't perform certain diagnostic tests. Perhaps someone has actually had this problem fixed by a transmission shop and can share the results. I would like to rebuild the entire valve body eventually, but if I can simply replace the PCS for now and fix the immediate problem that would be great.
12-25-2006, 10:47 AM
DTC P0742 means the TCC (Torque Convertor Clutch) is stuck on. Type "A" DTC thats disables shift adapts and forces the TCC to be commanded on. Also, may disable OD (4th). Most likely the TCC-PWM solenoid actually being stuck mechanically or could be the PCS or both. A supporting DTC of P1811 may confirm it is a PCS. If you go through all the trouble of getting the issue resolved then both TCC-PWM and PCS solenoids should be replaced.
Replacing the PCS, other solenoids or doing any valve body work is not typically DIY but can be done DIY. Shops like Cottmans charge around $550-$600 with parts but will try hard to talk you into a rebuild.
The TCC signal originates at the Powertrain Control Module (PCM) and inputs the tranny at the 20 way umbilical connector located top driver's side (left). Pin T (brown) and E (pink). Color coding to and within may vary.
Here is a general procedure applicable to any GM car with the 4T65E autotransaxles just to access the side cover assembly. This is just to get the side cover off to replace the solenoid. Time ranges from around 8 hours - 16 hours depending on shop facilities, tools, lifting equipment and patience level.
Disconnect the battery ground (negative) cable. Refer to Battery Negative Cable Disconnect/Connect Procedure in Starting and Charging.
Remove the throttle body air inlet duct. Refer to Air Cleaner Intake Duct Replacement in Powertrain Management.
Install the engine support fixture. Refer to Engine Support Fixture.
Remove the engine mount strut. Refer to Engine Mount Strut Replacement in Engine.
Raise and support the vehicle. Refer to Vehicle Lifting.
Remove the left front wheel. Refer to Tire and Wheel Removal and Installation in Steering and Suspension.
Remove the left engine splash shield. Refer to Splash Shield Replacement - Engine in Body and Frame.
Remove the stabilizer shaft links from the lower control arms. Refer to Stabilizer Shaft Link Replacement in Steering and Suspension.
Remove the left tie rod end from the steering knuckle. Refer to Steering Knuckle Replacement in Steering and Suspension.
Remove the wheel speed sensor harness connector. Refer Wheel Speed Sensor Jumper Harness Replacement (Front) in Brakes and Traction Control.
Remove the left lower ball joint from the left steering knuckle. Refer to Steering Knuckle Replacement in Steering and Suspension.
Disconnect the left drive axle from the transaxle. Refer to Wheel Drive Shafts Replacement (Left) or Wheel Drive Shafts Replacement (Right).
Secure the drive axle to the steering knuckle/strut. Caution: Failure to disconnect the intermediate shaft from the rack and pinion stub shaft can result in damage to the steering gear and/or damage to the intermediate shaft. This damage may cause loss of steering control which could result in personal injury.
Remove the pinch bolt at the intermediate steering shaft. Refer to intermediate Steering Shaft Replacement in Steering and Suspension.
Remove the intermediate shaft from the steering gear. Refer to Intermediate Steering Shaft Replacement in Steering and Suspension.
Disconnect the three-way catalytic converter pipe to the right (rear) exhaust manifold. Refer to Catalytic Converter Replacement in Powertrain Management.
Support the right side of the frame with jackstands.
Support the left side of the frame with jackstands.
Remove the transaxle mount bracket. Refer to Automatic Transmission Mount Bracket Replacement.
Remove the transaxle mount. Refer to Automatic Transmission Mount Replacement.
Loosen the engine mount lower nuts. Refer to Engine Mount Replacement (Front) and Engine Mount Replacement (Rear) in Engine.
Loosen the right side frame to body bolts. Refer to Frame Repair in Frame and Underbody.
Remove the left side frame to body bolts. Refer to Frame Repair in Frame and Underbody.
Adjust the jackstand to the lower left side of the frame.
Position the drain pan under the transaxle.
Remove the wiring harness connector.
Remove the case side cover bolts.
Remove side cover.
Pressure control (PCS) and TCC-PWM solenoids are located on the left hand side of the valve body.
During reassembly use new side cover gaskets.
BTW - When was the tranny last serviced? Pan drop replacing ATF and screen filter.
12-25-2006, 02:50 PM
Thanks for the advice bnaylor, I am pretty confident that I can perform the work myself. I'm armed with all the OE shop documentation along with the ATSG manual for this transmission and a nice set of tools including an engine crane. My only frustration is not having a Tech 2 scan tool, I'm debating whether or not I should try to line up the money to just buy one before attempting this repair. If people on here express a high enough level of confidence that the problem lies in either the TCC solenoid or the pressure control solenoid, then I'll probably skip the Tech 2 and just target those for replacement perhaps also the boost valve. Unfortunately my 350+ dollar autoenginuity scan tool doesn't access any of the transmission functions it claims to on their website. Extremely frustrating! I still need to sit down and figure out what sort of test I can contrive to observe the failure. I need to think about how the switch should be positioned under various conditions and watch to see if it is reacting properly. I'm assuming that the problem is not the TCC switch itself, that in fact the switch is correctly indicating no TCC release pressure when there should be. Essentially if it were just a failed switch I would expect to see the symptoms disappear immediately after clearing the faults from the computer, given that the computer should then operate the transmission normally until it recognizes the fault again.
12-25-2006, 03:36 PM
Solenoid problems can be electrical or the hydraulic mechanical portion of the valve. The TCC circuit is not that easy to troubleshoot without a proper scan tool like a GM Tech II. The problem is when the DTC sets you lose TCC lock/unlock functions and OD so even a road test may not reveal anything useful. Here is one of the best threads we have posted by Flatrater, one of our GM Moderators that may be helpful concerning what goes on with these valves mechanically:
Here is a P0742 problem that was resolved by a simple tranny service: <--Lucky!
As long as you have the confidence level and the equipment for the job then go for it. I've done a PCS job in a '97 Grand Prix GTP (4T65E-HD) over a weekend and by Monday it was working fine. It was a PITA but doable. Just for general principle I replaced all solenoids to include PCS, TCC-PWM, and the two shift solenoids and installed a shift kit.
Good luck and let us know how it turns out.
12-26-2006, 04:09 AM
Ok, I have some new diagnostic information to consider, I was able to get my autoenginuity software to give me access to the transmission data. Essentially I can watch the 1-2 and 2-3 shift solenoids working as I drive, along with the torque converter duty cycle, converter slippage, TCC pressure application, 1-2 shift time, 2-3 shift time, and 3-4 shift time. Everything seems to be working properly including the TCC status, theres no indication that it is stuck either on or off at this point, it reacts normally as I drive. What I am seeing is a long 1-2 shift around (.4 - .6s) and no 3-4 shift. When the computer activates the shift solenoids to indicate it is attempting to shift to 4th I get no actual shift. What I feel at that point is a surging in the powertrain and I get a whining or humming sound from the front driver's side area under the hood. From what I think I understand at this point it seems to make sense to me that if the pressure control solenoid has failed in some way that it would be reducing the pressure throughout the valve body it could cause the 1-2 solenoid to be reacting sluggishly causing the poor 1-2 shift and the loss of the 3-4 shift. It also makes sense that the low pressure throughout the valve body could result in a sluggish or sticky TCC release at times, perhaps causing the original but seemingly rare conditions for setting P0742. Tommorrow I am going to do another test drive with someone else monitoring the pressure control solenoid data, I'm hoping to catch it reacting differently from how it was commanded, although as bnaylor pointed out the problem could also be a mechanical valve failure such as a leak past an O-ring or a stuck mechanism. Please remember that this is the first time I have ever attempted to understand the detailed workings of any automatic trasmission. Hopefully someone can poke holes in my logic, let me know if I'm on the right track here. Thanks
12-26-2006, 10:08 AM
If you are going to get into detailed troubleshooting of the PCS then you could run the line pressure tests. Checkout page 120 of the ATSG SM. It shows the minimum and maximum line pressure specs depending on what gear the shifter is in and where to connect the pressure gauge.
12-27-2006, 06:58 PM
Just to give an update on my repair process, I received a used valve body assembly today for this transmission which I purchased on ebay and I also ordered a line pressure test kit so I can check the pressures at the service port. After getting my used valve body today, I completely disassembled the whole thing very carefully for practice. I wanted to get my hands on these parts without messing with my own transmission, I've learned a whole lot about how it works and how it is constructed. The ATSG manual came in handy in order to identify the components, but it was surprisingly straight forward to take everything apart. I took numerous pictures of the assembled body before taking anything apart so that I could recall the proper location of the clips and other components.
12-28-2006, 04:46 AM
At this point I've decided that the best course of action is to remove the transmission from the car, rebuild the valve body, replace the 4th gear clutch pack and re-assemble everything very carefully with new gaskets. The valve body will get new updated valves from sonnax and have all four solenoids replaced along with new O-rings wherever applicable. I will also ensure that the accumulator assembly in the pan area is properly sealed by removing it and replacing the various seals and/or gaskets. I'll also remove the torque converter and replace the O-ring perhaps even the converter itself if I can find a good replacement unit at a reasonable price. I'll disassemble the final drive assembly and inspect for damage or worn parts and check all of the toleranaces, particularly on the sun gears. Obviously I'll install a new filter and flush the cooler lines while the tranny is removed, I'll also check the fittings for any trapped debris. Ive purchased a brand new craftsman torque wrench to ensure absolutely perfect torquing of all bolts upon re-assembly. I already have two crafstman torque wrenches but they're probably out of calibration from heavy use.
I have two main questions at this point. First, what is the best way to support the engine when I drop the frame if I don't have an engine support fixture, or should I get/construct some sort of fixture? Second, if I wanted to do a complete rebuild, what are the essential tools I need, particularly to disassemble the clutches? So many of the specific tools used throughout the ATSG book seem like they could be substituted for more basic tools. The clutch assemblies look very intimidating to me and I've been avoiding the thought of a full re-build, presuming those things are not in bad shape, in a worst case scenario I might have destroyed the 4th gear clutch but that looks fairly easy to replace so my plan is to just do it to be sure. Can anyone see anything wrong with what I am planning to do?
12-29-2006, 12:39 PM
I recently rebuilt the 4T60E on my 93 Lesabre. Much of what I did is applicable to the 4T65E you are dealing with on your 2000 Lesabre. Before the rebuild I had a pretty good idea what the problem was. I had the common cold start problem due to a bad seal in the input clutch housing. But I went ahead and replaced all the seals using the rebuild kit. It's such a pain to remove and replace, why not do it all. I also had a few clutch plates that were worn from slippage and I replaced them too. Since I did not feel like the valve body was the problem. I did not remove the valves - I just cleaned it good. I also used the existing solenoids since they were working just fine. I felt this introduced less risk into the process.
My most inportant tool was a very good transmission jack. This is a must if you do not have a lift and plan on doing the work by yourself. With the help of the transmission jack, I was able to remove and replace the transmission by myself.
I did not use any of the special tools shown in the ATSG manual. I just fabricated what I needed - spring compressors, seal protectors, etc. It is a long and challengeing effort that you have before you, but in my case, it was a great learning experience and I do not regret doing it. I plan on getting many more miles out of my 93.
As far as supporting the engine, I used 2 by 4 lumber instead of a real engine support. I doubled up the front 2 by 4 and used a single for the rear. I used long eye bolts, nuts, and washers to connect the 2 by 4 to the engine support brackets. Make sure you use good quality lumber here and expect a little sagging since the engine is heavy.
On your second question, if I were going to all the trouble to remove and replace the transmission I would replace ALL the seals and gaskets and inspect all the clutches for wear and replace as necessary - especially considering the mileage on your car. But you are correct - the 4th clutch is easy compared to the input clutch housing.
12-31-2006, 11:14 PM
After speaking with a local transmission shop, I have narrowed down the failure to either a stripped out 4th clutch hub assembly or a failed/sticky/leaky valve in the valve body. Based on the fact that the car does seem to be shifting fairly normally while in 3rd I am sort of leaning towards the idea that the 4th gear clutch hub shaft splines are stripped. The guy at the local tranny shop says he's seen a lot of the 4t65e's with that problem. I had recognized the possibility that there could be a problem with the 4th clutch assembly before speaking with the shop and I had already planned to take it apart during my valve body overhaul. He believes the TCC code was tripped at the moment when the clutch hub shaft splines finally failed. Such a catastrophic failure probably confused the heck out of the computer and caused the code to trip. It is hard for me to believe that there is a problem with the TCC since I have driven the car extensively with my diag software and have never observed the TCC behaving abnormally. I've probably driven about 300 miles since clearing the TCC code, never to have it return, but I have absolutely no 4th gear. I did get my transmission line pressure gauge in the mail recently so I'll probably test the pressure at the service port to make sure it is within spec. If the line pressure checks ok then I'll probably go ahead and let the tranny shop worry about this one. The bottom line is that I really don't want to dive into a full rebuild project on my only car at this point. I'll get this fixed by the shop for now and then buy a used 4t65E on ebay to rebuild in my spare time. That way by the time something else fails in this transmission I'll have a freshly rebuilt unit to replace it with, hopefully even find someone to dyno my replacement before I install it. I've learned enough in diagnosing this problem to have a lot more confidence doing a rebuild on a spare tranny. Thanks for all the help and advice I'll let everyone know how it turns out. Unfortunately I may end up starting a new thread on an engine problem that seems to be getting worse, thanks again for the tranny help.
01-01-2007, 11:58 AM
If your scanner did not detect a P1811 DTC then a mechanical problem with the 4th clutch and spline is a possibility. Be sure to get the new hardened spline that is out for the 4T65E. The old one is garbage. Good luck.
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