UKcat Posted September 23, 2007 Report Share Posted September 23, 2007 HELP!!!! Driving my 1998 STS today; pulled out of a parking lot onto the highway; stopped to turn on to the parkway; drove 5 miles; no problems; everything just peachy. Stopped at the exit ramp; pulled out onto the road; transmission shifted hard in both gears; SCARED ME!!!; noticed that the message center said "service transmission". Didn't know what to do; 3 miles from home; no fluid trailing; no strange noises, so I limped on home slowly; shifted hard each time that I had to stop and start; 3 times. Got home; ran the codes; only thing that was current that is relative, it seems, was PCM P0748. I looked this up on my list; it says pressure control solenoid circuit electrical. What the heck is that???? Is it something that we can fix? Please don't tell me that we have to go back to the dealer. I just had the dreaded head gasket repair job done; I can't stand much more at this point. Is this something related to having the engine and tranny pulled? Don't have a clue; reaching for straws here. PLEASE HELP!!!!! My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted September 23, 2007 Report Share Posted September 23, 2007 The Pressure Control Solenoid Valve (PC Sol. Valve) regulates actuator feed fluid passing through the solenoid into torque signal pressure. The Powertrain Control Module (PCM) uses a pulse width modulated signal in order to control the torque signal pressure. The PCM compares various inputs in order to determine the appropriate pressure for a given load. The PCM varies the current to the PC Sol. Valve from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure. An internal current monitor within the PCM provides feedback in order to determine actual PC Sol. Valve current draw. If the PCM detects a commanded current draw that differs from the actual current draw by more than a calibrated value, then DTC P0748 sets. DTC P0748 is a Type C DTC. Conditions for Setting the DTC No Incorrect Gear Ratio DTC P0730. No Maximum Adapt and Long Shift DTC P1811. The system voltage is 10-17 volts. The engine run time is greater than 1 second. The difference between the commanded PC Sol. Valve current and the actual PC Sol. Valve current is 0.05 amps or more for 2 seconds. Action Taken When the DTC Sets The PCM does not illuminate the Malfunction Indicator Lamp (MIL). SERVICE VEHICLE SOON, SERVICE TRANSMISSION displays on the Driver Information Center (DIC). The PCM commands maximum line pressure. The PCM disables steady state adapts. The PCM disables upshift adapts. The PCM disables garage shift adapts. DTC P0748 is stored in the PCM history. Conditions for Clearing the DIC/DTC The PCM clears the DIC when the condition no longer exists. The commanded PC Sol. Valve current and the actual PC Sol. Valve current are within 0.05 amps of each other for 2 seconds. A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported. The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM. Diagnostic Aids Inspect the wiring at the PCM, the transmission 20-way connector and the PC Sol. Valve connector for the following conditions: A bent terminal A backed out terminal A damaged terminal Poor terminal tension A chafed wire A broken wire inside the insulation Moisture intrusion When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
JimD Posted September 23, 2007 Report Share Posted September 23, 2007 P0748 (PC solenoid circuit electrical) is the only related code and it the cause of your hard shifts (defaults to maximum line pressure). It could be a wiring or connector problem at the PCM connectors OR the large-round connector the leads to the transmission. If the pressure control solenoid has failed, the cradle has to be dropped far enough to access the side cover to replace the solenoid. Do not let anyone sell you a tansmission "overhaul"; an overhaul is not necessary. And it would a fine idea to replace the TCC solenoid (while the transmission is open) if it becomes necessary to replace the pressure control solenoid. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
UKcat Posted September 23, 2007 Author Report Share Posted September 23, 2007 Thanks guys. We are waiting for the car to cool down before we look to see if any connections are loose or anything. I just hope it is as simple as that. It would be nice if it was just a loose wire or connection or a simple module that we could replace ourselves. My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
Texas Jim Posted September 23, 2007 Report Share Posted September 23, 2007 Thanks guys. We are waiting for the car to cool down before we look to see if any connections are loose or anything. I just hope it is as simple as that. It would be nice if it was just a loose wire or connection or a simple module that we could replace ourselves. Since the engine was recently worked on... it may be that they didn't plug the harness back together good enough. Check the commectors at the transmission REAL WELL. Link to comment Share on other sites More sharing options...
BodybyFisher Posted September 24, 2007 Report Share Posted September 24, 2007 Yes clean the plug and re-seat it. When I did my ISS Speed sensor in the side pan, I replaced my pressure solenoid and the TCC solenoid while I was there, here is a photo of the solenoids, they are in the upper right of the upper valve body in this photo, I should have replaced the thrust bearings also, I stupidly neglected to replace them: Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
UKcat Posted September 25, 2007 Author Report Share Posted September 25, 2007 Well, I started the car this afternoon to pull it in the lower garage; the service transmission message was gone, so I drove it down the road; shifted and ran fine for about 3 miles. I turned around to head back to the house and it shifted hard and the message came back on. I checked the plugs and connections as best as I could. I did not find anything loose or broken that I could see. I guess it is back to the dealer for me. I just don't know enough about this car to work on it. If this turns out to be expensive, I will be regretting the head gasket repair big time!!! My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
BodybyFisher Posted September 25, 2007 Report Share Posted September 25, 2007 Well, I started the car this afternoon to pull it in the lower garage; the service transmission message was gone, so I drove it down the road; shifted and ran fine for about 3 miles. I turned around to head back to the house and it shifted hard and the message came back on. I checked the plugs and connections as best as I could. I did not find anything loose or broken that I could see. I guess it is back to the dealer for me. I just don't know enough about this car to work on it. If this turns out to be expensive, I will be regretting the head gasket repair big time!!! Were you able to take the tranny plug apart and reset it? Here is what the tranny side of the plug looks like Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
UKcat Posted September 25, 2007 Author Report Share Posted September 25, 2007 Is this plug the round, 20 pin plug that is visible from the top side under the hood?? I did take that plug apart and look at it; I didn't see anything wrong with it; not sure if it was the right one or not. Sorry to sound uninformed; I just don't know much about this car. We have had it a long time now; wish I had taken more time to inform myself about it!! I can work on my GTO; it's not complicated like this one is My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
BodybyFisher Posted September 25, 2007 Report Share Posted September 25, 2007 Be careful, there is a plug for the injector rail and a plug for the tranny, they are similar... Look at the location of the plug in the photo I posted above, Mike Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
UKcat Posted September 26, 2007 Author Report Share Posted September 26, 2007 O.K fellas, we need your help here. The caddy dealer, I think, is trying to stick us. He says he thinks the pressure control solenoid is bad, wants $1500.00 to replace it and the wiring and "check everything out". AIN'T GONNA HAPPEN! So far, you have indicated this should be a pretty simple procedure; now, I need step by step directions; maybe I can do this myself. Please help. My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
UKcat Posted September 27, 2007 Author Report Share Posted September 27, 2007 I still need a little help here; anybody got any more info. for replacing these solenoids??? We are going to try to do it ourselves, with your help! My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
UKcat Posted September 27, 2007 Author Report Share Posted September 27, 2007 We have located the parts; I am still waiting for your help with this matter. Won't somebody please tell us what to do??? I know you said to drop the cradle to access the side compartment and that they solenoid would be inside there; is that all there is to it???????????? My "other car" 1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car *Get well soon, John Force!!!* Link to comment Share on other sites More sharing options...
BodybyFisher Posted September 27, 2007 Report Share Posted September 27, 2007 Here is my thread on replacing the ISS speed sensor, this should give you some help http://caddyinfo.ipbhost.com/index.php?sho...hl=speed+sensor Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
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