Transmission Problems

STANLEY SOLOMON

MEMBER
1998 CHEVROLET TRUCK
V8
4WD
AUTOMATIC
104,000 MILES

I'm having a problem with the Transmission shifting. I thought the trans. Might be bad so I replaced it and I'm still having the same problem with the shifting. The Check Engine Soon Light stays on and it just will not go into O/D and somtimes it doesn't want the upshift from 2nd to 3rd. I've replaced all the Modules and changed the fluid and filter 3 times so far. I've been told that it could be the Ignition Switch. Could that possibly be the problem? I don't know what else to do. Can you help? Thanks, Stanley

5 Replies

BRIAN 1

MECHANIC
1,030 POSTS

What happens is the exhaust system became plugged which changes the vacuum reading to the computer which makes it think the truck is under heavy load all of the time. Please check out this guide to confirm the failure. BTW what is the code?

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please let us know what you find.

Cheers, Ken

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Tuesday, January 20th, 2009 AT 11:37 AM

STANLEY SOLOMON

MEMBER
7 POSTS

The code PO758 is what comes up. What does that mean?

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Wednesday, January 21st, 2009 AT 1:26 PM

BRIAN 1

MECHANIC
1,030 POSTS

P0758 is 3-2 shift solenoid circuit electrical, lets star by what model is the vehicle and is this a 4L60E or 4L80E trans. What modules did you replace and why did you replace the trans, was it a remaned, aftermarket or OEM trans, or did somebody rebuild it? Wright now I want you to check #20 trans fuse in the i/p fuse block, check if the fuse is blown first. It could be just a bad shift solenoid, an open or short to ground in ignition feed circuit 1020 or a bad VCM. Post back with what you find and will advise. Also need engine size.

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Wednesday, January 21st, 2009 AT 1:48 PM

STANLEY SOLOMON

MEMBER
7 POSTS

I replaced the original with a trans. Out of a 95 Suburban that I drove and the trans. Worked perfect until I put in my truck and started from begining to act up like the 98 trans. It has troubles shifting in different gears. Sometimes 2nd to 3rd and again into O/D. I changed the solenoids out of the 98 after the 95 trans didn't shift right. What else can I do?

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Wednesday, January 21st, 2009 AT 2:33 PM

BRIAN 1

MECHANIC
1,030 POSTS

You can start by checking the trans fuse,see if its blown.from there it could still be a shift solenoid,just because you switched them out of an old trans doesn't mean they cant go bad,it could also be debris/dirt in the valve body.it could be an open or short to ground in ignition feed circuit 1020 (PNK) to the 3-2 SS Valve Assembly.it could be in the VCM. You will need a good scan tool to look at shift data and perform bi-direction tests on the shift solenoids to see if there working,also a trans out of an older vehicle might have been fine until you put it in the vehicle its in now,but could still develop problems.you need to do some testing,if not everything will be a guess.

Please use this guide and these wiring diagrams to check the wiring.

https://www.2carpros.com/articles/how-to-check-wiring

also make sure all of the fuses are good.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (Below)

Please let us know what you find.

Cheers

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