Transmission line pressure problems, codes P1571 and P0748. HELP!
02-28-2008, 01:53 PM
#1
Melting Slicks
Thread Starter
Transmission line pressure problems, codes P1571 and P0748. HELP!
I am in the middle of trying to diagnose a problem I am having with my transmission. I am getting the following codes: P0748 and P1571. The problem is the transmission line pressure is maxed out and bangs when it shifts and goes into gear forward or reverse. It shifts normally up and down, but it bangs hard like the line pressure is maxed out. I had a well known local tuner look at it and he added some torque management back then also tried to adjust the line pressure. It didn't work. He referred me to a transmission shop that pulled these codes and thought I had a bad pressure control soleniod. We replaced that, it didn't work. He then thinks I have a bad wiring harness, either a short or a bad connector internally in the transmission, we replaced the harness, it didn't work. I then took the car back because he was wasting my time. I believe it's either a short or bad connection from the TCM to the transmission or from the PCM to the TCM. I printed out the flow chart for the diagnostics on these codes and it could also be that either the PCM or TCM is bad. I looked at the wires and connectors to both and didn't see any visible problems with the insulation or wires, for what it's worth. What do you guys think is the best way to proceed? Thanks in advance for any help.
Last edited by Rhode Warrior; 02-28-2008 at 02:00 PM.
02-28-2008, 07:56 PM
#3
Burning Brakes
P0748 is usually caused by lowering the force motor current tables. The force motor tables should be left stock except for the 100 psi column.
The 100 psi column should be changed to 0. The shift pressure table is were you firm up the shifts.
P1571 is the Traction Control Torque Request Circuit. But correct the P0748 code first, as it may be setting off P1571.
Russ Kemp
The 100 psi column should be changed to 0. The shift pressure table is were you firm up the shifts.
P1571 is the Traction Control Torque Request Circuit. But correct the P0748 code first, as it may be setting off P1571.
Russ Kemp
02-28-2008, 09:24 PM
#4
Melting Slicks
Thread Starter
P0748 is usually caused by lowering the force motor current tables. The force motor tables should be left stock except for the 100 psi column.
The 100 psi column should be changed to 0. The shift pressure table is were you firm up the shifts.
P1571 is the Traction Control Torque Request Circuit. But correct the P0748 code first, as it may be setting off P1571.
Russ Kemp
The 100 psi column should be changed to 0. The shift pressure table is were you firm up the shifts.
P1571 is the Traction Control Torque Request Circuit. But correct the P0748 code first, as it may be setting off P1571.
Russ Kemp
02-29-2008, 01:08 AM
#5
Safety Car
Are the two codes you listed the ONLY codes the car is throwing, or have you checked recently for others.
Display your DTC data on the DIC and post ALL the codes the car is displaying.
What diagnostics did you try for the P0748 ??? The Service Manual lists a series of tests that you should perform to help in figuring out if it is in the wiring, the Pressure Control (PC) Solenoid, or the PCM. Unfortunately, some of the tests (such as step 2) require a Tech2 scanner, did either of the two shops yoou tried have a Tech2?
Post the codes ... let's see what you have ....
Display your DTC data on the DIC and post ALL the codes the car is displaying.
What diagnostics did you try for the P0748 ??? The Service Manual lists a series of tests that you should perform to help in figuring out if it is in the wiring, the Pressure Control (PC) Solenoid, or the PCM. Unfortunately, some of the tests (such as step 2) require a Tech2 scanner, did either of the two shops yoou tried have a Tech2?
Post the codes ... let's see what you have ....
02-29-2008, 01:39 AM
#6
Melting Slicks
Thread Starter
Are the two codes you listed the ONLY codes the car is throwing, or have you checked recently for others.
Display your DTC data on the DIC and post ALL the codes the car is displaying.
What diagnostics did you try for the P0748 ??? The Service Manual lists a series of tests that you should perform to help in figuring out if it is in the wiring, the Pressure Control (PC) Solenoid, or the PCM. Unfortunately, some of the tests (such as step 2) require a Tech2 scanner, did either of the two shops yoou tried have a Tech2?
Post the codes ... let's see what you have ....
Display your DTC data on the DIC and post ALL the codes the car is displaying.
What diagnostics did you try for the P0748 ??? The Service Manual lists a series of tests that you should perform to help in figuring out if it is in the wiring, the Pressure Control (PC) Solenoid, or the PCM. Unfortunately, some of the tests (such as step 2) require a Tech2 scanner, did either of the two shops yoou tried have a Tech2?
Post the codes ... let's see what you have ....
02-29-2008, 02:04 AM
#7
Safety Car
The C5 is a unique car .... you don't need a scanner to either read or delete the DTC codes. In fact the C5 will display ALL the codes in ALL the cars computers on the DIC. Scanners normally can only read Powertrain codes, not codes posted in computers such as the EBCM.
Go here for instructions for displaying the DTC and also deleting them if you want to.
https://www.corvetteforum.com/techti...D=26&TopicID=1
Post tomorrow what you find,
Good luck,
Go here for instructions for displaying the DTC and also deleting them if you want to.
https://www.corvetteforum.com/techti...D=26&TopicID=1
Post tomorrow what you find,
Good luck,
Last edited by BlackZ06; 02-29-2008 at 02:07 AM.
04-03-2008, 07:01 PM
#8
Melting Slicks
Thread Starter
OK, finally got a chance to put the battery back in and check the codes.
I went in and cleared all codes. Then started it, shut it off and checked it. I did it a few times, resetting the codes every time. Each time I started it, whether or not I put it in gear, I get the following codes:
P0748 HC
P1571 H (this history code comes back every time)
38 RTD no comm
99 HVAC no comm
I went in and cleared all codes. Then started it, shut it off and checked it. I did it a few times, resetting the codes every time. Each time I started it, whether or not I put it in gear, I get the following codes:
P0748 HC
P1571 H (this history code comes back every time)
38 RTD no comm
99 HVAC no comm
04-04-2008, 04:04 PM
#10
Melting Slicks
Thread Starter
Does anyone know where I can get a schematic of the pin connectors on my PCM and transmission wiring harness? Seems like a logical place to start. Thanks in advance.
04-04-2008, 04:49 PM
#11
Tech Contributor
Member Since: Oct 1999
Location: Charlotte, NC (formerly Endicott, NY)
Posts: 40,096
Received 8,930 Likes
on
5,334 Posts
Here is some Tech Bulletin info on the P1571 problem. This is for 97s only.
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
Last edited by Bill Dearborn; 04-04-2008 at 05:19 PM.
04-04-2008, 05:50 PM
#12
Melting Slicks
Thread Starter
Here is some Tech Bulletin info on the P1571 problem. This is for 97s only.
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
Thanks for posting this. This did turn up in my forum search and I think this is exactly what's happening with the 1571, but it's the P0748 code that I believe is screwing up my line pressure. I think it's either a short, or a break in a wire, or maybe it's just the PCM not putting out the proper voltage. I'm still trying to narrow it down.
04-23-2008, 05:19 PM
#19
Race Director
Here is some Tech Bulletin info on the P1571 problem. This is for 97s only.
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
History DTC P1571 Stored and Will Not Clear #PI00219 - (Jul 2, 2002)
History DTC P1571 Stored and Will Not Clear
.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
Vehicle may have a DTC P1571 [ASR (Automatic Slip Regulation) Desired Torque Circuit] stored in history that cannot be cleared. DTC C1277 (Requested Torque Signal CKT Malfunction) is NOT present and there is No Service Vehicle Soon lamp or powertrain related lamps on.
Recommendation/Instructions:
This is a normal condition. All 1997 YBs will have a DTC P1571 stored as history in the PCM that cannot be cleared. If P1571 is current, follow the trouble table in SI Document Number 101551. It should be noted that the schematic in this document incorrectly lists a ckt 449 dk blu/wht and calls it Real Time Dampening. This ckt is not present and should be ignored for both 97 and 98 (Document Number 203769) model year SI. A Service Information Update has been submitted.
Send me a PM with your e-mail address and I will forward a MS Word file with the connector pin outs for a 97.
Bill
05-03-2010, 06:40 PM
#20
Melting Slicks
Thread Starter
I thought the P0748 line pressure problem was gone but it reared it's ugly head again and this time I was able to find the problem! Last time, I brought it to a local Corvette tuner who shall remain anonymous. He plugged in his laptop, played around with the line pressures and condemned the transmission. He recommends a transmission guy and I take it to him. He reads the code and suspects the solenoid valve. Replaces it, same code. Following the DTC matrix, he then suspects the internal harness in the transmission. Replaces it, same code. He then says it has to be a broken wire and doesn't know how long it will take to find the problem. I had a enough and I pick up my car, $250.00 dollars lighter in the wallet, with the same problem. The problem goes away after a while then comes back intermittently so I suspect the PCM. Fast forward one year the code starts up again last month.
I bought a set of manuals and a jumper harness for the 20 pin connector and started following the test procedures. I started at the transmission and tried to take an ohm reading between terminals C & D (high and low solenoid pressure wires, red with black stripe and blue with white stripe.) No resistance, no continuity. Fine, moving right along, take a reading at the same terminals on the PCM blue connector (terminals 36 and 39). Same readings. I suspected the pins on the harness connector so I disassembled the blue connector and checked for corrosion, loose pin, etc. Everything looked fine. I am now suspecting that there is a break in the wire between the PCM and the transmission. I removed the passenger side header to replace the header gasket and I have a clear view of the harness and can see it's very securely routed from the factory and it runs the legnth of the torque tube and looks very well protected. I decide to trace the harness manually and hook up my meter to terminals 36 & 39 on the blue PCM connector harness. I then hooked up the test harness at the 20 pin connector on the transmission and placed a jumper between the C & D terminals. I then start massaging the harness, listenin for the beep. I move every part that I can reach and get no results from the connector on the transmission all the way back to where it comes out behind the header. I partially untaped the harness because even though it shows the wires running directly to the PCM in the manual, they run to another 20 pin connector, then back to the PCM. As soon as I moved that connector, which is located on the passenger fender kind of behind the fuse box, "BEEP".
I wiggle the connector around some more "BEEP, BEEP". Music to my ears.
I lightly pulled on both red and blue wires from each side of the connector and the blue/white female connector pulls right out of the plug. Problem solved. I cut both sets of wires from the harness just to be on the safe side, then soldered and shrink wrapped each wire. Reset the codes, (which were tripping every time I put it in gear this time around) started it up and put it in gear a few times. Shut the car down, tried it a few more times. No clunk, no codes.
Time for a cold one, I deserve it.
I bought a set of manuals and a jumper harness for the 20 pin connector and started following the test procedures. I started at the transmission and tried to take an ohm reading between terminals C & D (high and low solenoid pressure wires, red with black stripe and blue with white stripe.) No resistance, no continuity. Fine, moving right along, take a reading at the same terminals on the PCM blue connector (terminals 36 and 39). Same readings. I suspected the pins on the harness connector so I disassembled the blue connector and checked for corrosion, loose pin, etc. Everything looked fine. I am now suspecting that there is a break in the wire between the PCM and the transmission. I removed the passenger side header to replace the header gasket and I have a clear view of the harness and can see it's very securely routed from the factory and it runs the legnth of the torque tube and looks very well protected. I decide to trace the harness manually and hook up my meter to terminals 36 & 39 on the blue PCM connector harness. I then hooked up the test harness at the 20 pin connector on the transmission and placed a jumper between the C & D terminals. I then start massaging the harness, listenin for the beep. I move every part that I can reach and get no results from the connector on the transmission all the way back to where it comes out behind the header. I partially untaped the harness because even though it shows the wires running directly to the PCM in the manual, they run to another 20 pin connector, then back to the PCM. As soon as I moved that connector, which is located on the passenger fender kind of behind the fuse box, "BEEP".
I wiggle the connector around some more "BEEP, BEEP". Music to my ears.I lightly pulled on both red and blue wires from each side of the connector and the blue/white female connector pulls right out of the plug. Problem solved. I cut both sets of wires from the harness just to be on the safe side, then soldered and shrink wrapped each wire. Reset the codes, (which were tripping every time I put it in gear this time around) started it up and put it in gear a few times. Shut the car down, tried it a few more times. No clunk, no codes.
Time for a cold one, I deserve it.