4L60E with P0748 code
11-02-2014, 04:40 PM
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4L60E with P0748 code I have a ls1/4l60e swap and have a P0748 code set after a wide open throttle run. I have checked the wiring for that circuit and replaced the PCS too. I'am running a stock 2004 corvette tune in the ecm and have no other codes in it.
With the scanner on it after the wot run the pcs amperage goes to 0 and in turn you get the severe 1-2 upshift.
I can clear the code and go back out and drive and everything is normal until another wot run.
Now does ckt 1229? red/black in the schematic show 12v but after it set the code it only show 5v, is this normal or is it something in the ecm or else where.
Thanks for the input on this issue.
With the scanner on it after the wot run the pcs amperage goes to 0 and in turn you get the severe 1-2 upshift.
I can clear the code and go back out and drive and everything is normal until another wot run.
Now does ckt 1229? red/black in the schematic show 12v but after it set the code it only show 5v, is this normal or is it something in the ecm or else where.
Thanks for the input on this issue.
11-02-2014, 05:17 PM
#2
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First, various codes will cause the PCM to max the line pressure to reduce slippage in the trans.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
11-02-2014, 05:50 PM
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First, various codes will cause the PCM to max the line pressure to reduce slippage in the trans.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
(1228 is the blu/wht going to pcs from the ecm.)
Trans is from 98 ( I wondered the same as for the programing between 98 to 2004)
Will try you test and report back.
Thanks for the help.
11-02-2014, 07:14 PM
#4
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Your 5V now sounds like a clue. After the code the PCS current goes to 0 amps (max line pressure) and the voltage should therefore be +12V.
Here is my hypothesis: When you go WOT the PCM commands max line pressure by reducing the PCS current to Zero. Knowing the current is Zero, it checks the voltage and since it doesn't see anything close to 12V, it throws a code.
Perhaps a bad connection, perhaps a bad PCM, perhaps you measured the wrong pin.
Here is my hypothesis: When you go WOT the PCM commands max line pressure by reducing the PCS current to Zero. Knowing the current is Zero, it checks the voltage and since it doesn't see anything close to 12V, it throws a code.
Perhaps a bad connection, perhaps a bad PCM, perhaps you measured the wrong pin.
11-02-2014, 07:46 PM
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First, various codes will cause the PCM to max the line pressure to reduce slippage in the trans.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
What is circuit 1229? I don't memorize all circuit #s.
What year is the trans and what year is the PCM? Most '98 to '08 should be compatible, but kinda grasping for straws here.
Another interesting test would be to use a scanner to command max line pressure and see if you then immediately get a code.
But was a good idea.
12-21-2014, 01:09 PM
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Your 5V now sounds like a clue. After the code the PCS current goes to 0 amps (max line pressure) and the voltage should therefore be +12V.
Here is my hypothesis: When you go WOT the PCM commands max line pressure by reducing the PCS current to Zero. Knowing the current is Zero, it checks the voltage and since it doesn't see anything close to 12V, it throws a code.
Perhaps a bad connection, perhaps a bad PCM, perhaps you measured the wrong pin.
Here is my hypothesis: When you go WOT the PCM commands max line pressure by reducing the PCS current to Zero. Knowing the current is Zero, it checks the voltage and since it doesn't see anything close to 12V, it throws a code.
Perhaps a bad connection, perhaps a bad PCM, perhaps you measured the wrong pin.
I have also noticed that it happens when the trans temp. reaches between 150° and 160° F and as of lately it does not need to be WOT, it will fault out even idling.
Any input would be greatly appreciated. Thanks
12-21-2014, 01:39 PM
#7
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Just to summarize - P0748 is the code for the pressure control solenoid (PCS).
You already replaced the PCS.
Now you replaced the PCM.
The problem persists and seems to be getting more common.
You seem to know a lot about transmission diagnosing.
Sorry, but this is stumping me.
Have you checked the trans connector for corrosion or excessive moisture?
I would start with a resistance check from the PCS to the PCM. I would not expect much more than one Ohm.
Hmmm - just thought of a remote possibility.
IIRC the PCS changed somewhere around 2002. The earlier ones had two spade lugs for their connection, while the later ones have a snap on connector like the shift solenoids. My local trans mechanic told me he thought they were electrically slightly different. (But I have check that their resistance is the same.) I have used the new style with an older PCM, but not the other way around.
I doubt this is the problem, but I am grasping for straws here.
You already replaced the PCS.
Now you replaced the PCM.
The problem persists and seems to be getting more common.
You seem to know a lot about transmission diagnosing.
Sorry, but this is stumping me.
Have you checked the trans connector for corrosion or excessive moisture?
I would start with a resistance check from the PCS to the PCM. I would not expect much more than one Ohm.
Hmmm - just thought of a remote possibility.
IIRC the PCS changed somewhere around 2002. The earlier ones had two spade lugs for their connection, while the later ones have a snap on connector like the shift solenoids. My local trans mechanic told me he thought they were electrically slightly different. (But I have check that their resistance is the same.) I have used the new style with an older PCM, but not the other way around.
I doubt this is the problem, but I am grasping for straws here.
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12-21-2014, 02:17 PM
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Just to summarize - P0748 is the code for the pressure control solenoid (PCS).
You already replaced the PCS.
Now you replaced the PCM.
The problem persists and seems to be getting more common.
You seem to know a lot about transmission diagnosing.
Sorry, but this is stumping me.
Have you checked the trans connector for corrosion or excessive moisture?
I would start with a resistance check from the PCS to the PCM. I would not expect much more than one Ohm.
Hmmm - just thought of a remote possibility.
IIRC the PCS changed somewhere around 2002. The earlier ones had two spade lugs for their connection, while the later ones have a snap on connector like the shift solenoids. My local trans mechanic told me he thought they were electrically slightly different. (But I have check that their resistance is the same.) I have used the new style with an older PCM, but not the other way around.
I doubt this is the problem, but I am grasping for straws here.
You already replaced the PCS.
Now you replaced the PCM.
The problem persists and seems to be getting more common.
You seem to know a lot about transmission diagnosing.
Sorry, but this is stumping me.
Have you checked the trans connector for corrosion or excessive moisture?
I would start with a resistance check from the PCS to the PCM. I would not expect much more than one Ohm.
Hmmm - just thought of a remote possibility.
IIRC the PCS changed somewhere around 2002. The earlier ones had two spade lugs for their connection, while the later ones have a snap on connector like the shift solenoids. My local trans mechanic told me he thought they were electrically slightly different. (But I have check that their resistance is the same.) I have used the new style with an older PCM, but not the other way around.
I doubt this is the problem, but I am grasping for straws here.
As for connections they are all clean and corrosion free but that's where I'm thinking the problem is either in the harness in the trans or external.
Yes the PCS changed in 2003 and like you I think they are the same except for the connector.
As for grasping for straws I've been doing the same, even tried a resistor in the temp circuit so it would read a fixed temp. of 135°F and still the same problem.
I've taken some time away from it to clear my head but it's still haunting me.
Other reading around even suggests possible engine coolant sensor, throttle position sensor. and the manifold/ temp sensor in the trans.
05-12-2016, 01:27 PM
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I wish I knew more about this. I would think that someone else out the has had the same experience but no luck yet.
As for connections they are all clean and corrosion free but that's where I'm thinking the problem is either in the harness in the trans or external.
Yes the PCS changed in 2003 and like you I think they are the same except for the connector.
As for grasping for straws I've been doing the same, even tried a resistor in the temp circuit so it would read a fixed temp. of 135°F and still the same problem.
I've taken some time away from it to clear my head but it's still haunting me.
Other reading around even suggests possible engine coolant sensor, throttle position sensor. and the manifold/ temp sensor in the trans.
As for connections they are all clean and corrosion free but that's where I'm thinking the problem is either in the harness in the trans or external.
Yes the PCS changed in 2003 and like you I think they are the same except for the connector.
As for grasping for straws I've been doing the same, even tried a resistor in the temp circuit so it would read a fixed temp. of 135°F and still the same problem.
I've taken some time away from it to clear my head but it's still haunting me.
Other reading around even suggests possible engine coolant sensor, throttle position sensor. and the manifold/ temp sensor in the trans.
11-04-2016, 07:30 AM
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Did you ever solve your P0748 problem, I have the exact same problem as you, only on high engine load the code will set, can clear it and the truck drive fine until WOT. Wirings fine, replace the PCS, still nothing
11-04-2016, 10:27 AM
#12
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Unfortunately mvette86 has not posted anywhere on this forum since #8 above.
Shame people don't post updates even if it's just "sold the car" or "replaced the trans".
I have no suggestions beyond what I posted in #7 above; this issue has not come up since.
Shame people don't post updates even if it's just "sold the car" or "replaced the trans".
I have no suggestions beyond what I posted in #7 above; this issue has not come up since.
11-04-2016, 02:50 PM
#14
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If you replaced the PCS and are confident of the wiring/harness, then the PCM might be at fault. Ebay seller "SpareECM" has LS1 PCM for $89 and that includes "tuning" it with your VIN and with VATS and a few emission options either enabled or disabled.
11-08-2016, 08:24 AM
#18
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