Transmission P0742 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

Reply
 
 
 
Thread Tools Search this Thread
Old 10-20-2010, 11:57 AM   #1
Senior Member
True Car Nut
Thread Starter
 
xtremerevolution's Avatar
 
Join Date: Jun 2007
Location: New Lenox, IL
Posts: 2,478
Thanks: 0
Thanked 0 Times in 0 Posts
xtremerevolution is on a distinguished road
Default Transmission P0742

I've done some reading, but have found this error. Previously, the transmission threw a P0748. The transmission is slipping while engaging 1st gear.

My solution so far was to lower FMC values for low torque sections of the FMC tables in order to signal more pressure to the PCS, and the transmission no longer slips into 1st. I'm aware that this is a temporary fix as it shouldn't be slipping to begin with. It has been suggested that an accumulator seal can be to blame for this.

Right now my biggest concern is this P0742, because when it goes off, the transmission goes into limp mode and its very annoying to drive.

People are saying this can be a bad or stuck TCC switch, bad internal or engine wiring (which I will be testing), or a stuck/clogged PCS solenoid.

I'm planning on bringing this car into the garage to fix the above outlined problems. I need all the help I can get here. If I do drop the pan to replace the filter and gasket (which both need to be replaced), I will be be lowering the entire engine and trans to get the side cover off as well.

While I'm in there, what should I replace? Should I replace all of the solenoids? Should I replace the pressure switch manifold? Should I remove the valve body, and if I do, is there anything else I should replace as a preventative measure while I'm in there?

I'd like to have all of the information and all of the parts I need before I begin with this.
xtremerevolution is offline   Reply With Quote
Old 10-20-2010, 12:12 PM   #2
Senior Member
True Car Nut
Thread Starter
 
xtremerevolution's Avatar
 
Join Date: Jun 2007
Location: New Lenox, IL
Posts: 2,478
Thanks: 0
Thanked 0 Times in 0 Posts
xtremerevolution is on a distinguished road
Default

I just realized something. Is it at all possible that I've set the pressure too high and that its causing the TCC to stick on?
xtremerevolution is offline   Reply With Quote
Old 10-20-2010, 12:12 PM   #3
DINOSAURUS BOOSTUS

Expert Gearhead
 
BillBoost37's Avatar
 
Join Date: Mar 2005
Location: Enfield, CT
Posts: 41,391
Thanks: 0
Thanked 0 Times in 0 Posts
BillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of light
Default

How can we help you if you haven't done the testing we suggested on the wiring/soleniods to determine if you need to go into the sidecover?

I'm ready to help, but don't understand how to do so.

And yeah..sorry for being a bit of a jerk, but this morning there'* a multithread for one issue bonanza going on and you joined the Koolaid drinkers. =0)
BillBoost37 is offline   Reply With Quote
Old 10-20-2010, 12:24 PM   #4
Senior Member
True Car Nut
Thread Starter
 
xtremerevolution's Avatar
 
Join Date: Jun 2007
Location: New Lenox, IL
Posts: 2,478
Thanks: 0
Thanked 0 Times in 0 Posts
xtremerevolution is on a distinguished road
Default

Quote:
Originally Posted by BillBoost37 View Post
How can we help you if you haven't done the testing we suggested on the wiring/soleniods to determine if you need to go into the sidecover?

I'm ready to help, but don't understand how to do so.

And yeah..sorry for being a bit of a jerk, but this morning there'* a multithread for one issue bonanza going on and you joined the Koolaid drinkers. =0)
It started with the PCS solenoid, and I tested that already. The wiring to the PCM is good, the solenoid'* resistance is within spec.

I haven't yet tested the TCC solenoid for the same thing, but I'll be able to get to that today. Some of this is second nature for you guys, but not for me. I'm just learning about transmissions, so its still all fairly new. Also, this new TCC stuck code is very intermittent. Its not a constant code. It will go off randomly one day and not at all for another 2 days. I set the pressure back to stock settings in Utah while driving from LA to Chicago this past weekend, and it didn't go off at all the whole way here. Yesterday I decided to put the firmer tables back on because it was slipping into 1st, and it worked fine all day, till today on the way to work I got this code again. I can't tell if the pressure is at all even related. Lowering the FMC values to raise line pressure is also something I had not attempted in the previous thread, but the simple fact is that it works, and I thought that it might be of some relevance that it does work for those who know something about transmissions.

The only thing I have left to check as far as the slipping into 1st gear issue is that accumulator (is that what is called?) seal(*) when I drop the pan. I want to be prepared to have to go further if I find nothing wrong, which is why I created this thread.
xtremerevolution is offline   Reply With Quote
Old 10-20-2010, 12:46 PM   #5
Senior Member
True Car Nut
Thread Starter
 
xtremerevolution's Avatar
 
Join Date: Jun 2007
Location: New Lenox, IL
Posts: 2,478
Thanks: 0
Thanked 0 Times in 0 Posts
xtremerevolution is on a distinguished road
Default

Just a side note, it seems that this guy is having the same problem:

https://www.gmforum.com/1992-1999-91/tranny-swap-rebuild-options-293078/
xtremerevolution is offline   Reply With Quote
Old 10-20-2010, 12:51 PM   #6
Retired Senior Admin

Expert Gearhead
 
Danthurs's Avatar
 
Join Date: May 2006
Location: Sheboygan Wisconsin
Posts: 29,661
Thanks: 0
Thanked 16 Times in 13 Posts
Danthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to all
Default

If you manually shift in to 1st, do you have the same slippage? The problem cal also be worn clutches. When you drop the pan look at the magnet. Also, take out the shift modulator and open that up. It'* right there so you may as well check it. Check for smooth shiny cylinder walls. If you have that, sand with some 400 grit just to scuff it up. Inspect the O rings. I've seen adding a shift kit remove slipping mainly because it engages faster.
Danthurs is offline   Reply With Quote
Old 10-20-2010, 12:59 PM   #7
Senior Member
True Car Nut
Thread Starter
 
xtremerevolution's Avatar
 
Join Date: Jun 2007
Location: New Lenox, IL
Posts: 2,478
Thanks: 0
Thanked 0 Times in 0 Posts
xtremerevolution is on a distinguished road
Default

Quote:
Originally Posted by Danthurs View Post
If you manually shift in to 1st, do you have the same slippage? The problem cal also be worn clutches. When you drop the pan look at the magnet. Also, take out the shift modulator and open that up. It'* right there so you may as well check it. Check for smooth shiny cylinder walls. If you have that, sand with some 400 grit just to scuff it up. Inspect the O rings. I've seen adding a shift kit remove slipping mainly because it engages faster.
If I manually shift into 1st, it doesn't slip. It doesn't actually "slip" at all if you will. It just doens't engage 1st gear. You can sit there and as you accelerate, it will not have 1st engaged until it will just..."pop" into place and all 1st gear will engage. Once you are in 1st gear though, it doesn't slip.

I'll take out that shift modulator probably tonight and take a look. I suppose dropping the pan isn't that big of a deal.

I'll also look through that shift kit writeup and go ahead and do that as well. I'll report back once that'* done, although it still doesn't explain this P0742 code.
xtremerevolution is offline   Reply With Quote
Old 10-20-2010, 01:22 PM   #8
DINOSAURUS BOOSTUS

Expert Gearhead
 
BillBoost37's Avatar
 
Join Date: Mar 2005
Location: Enfield, CT
Posts: 41,391
Thanks: 0
Thanked 0 Times in 0 Posts
BillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of light
Default

That'* not really a slip you just described, but a bang start.
BillBoost37 is offline   Reply With Quote
Old 10-20-2010, 01:26 PM   #9
DINOSAURUS BOOSTUS

Expert Gearhead
 
BillBoost37's Avatar
 
Join Date: Mar 2005
Location: Enfield, CT
Posts: 41,391
Thanks: 0
Thanked 0 Times in 0 Posts
BillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of light
Default

BillBoost37 is offline   Reply With Quote
Old 10-20-2010, 02:17 PM   #10
Retired Senior Admin

Expert Gearhead
 
Danthurs's Avatar
 
Join Date: May 2006
Location: Sheboygan Wisconsin
Posts: 29,661
Thanks: 0
Thanked 16 Times in 13 Posts
Danthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to allDanthurs is a name known to all
Default

What your describing isn't the modulator. That sounds like the forward band. The solenoid to engage that is on the rear of the transmission near the diff cover, a little to the left of the cover. You will see what looks like a cup mounted on the back of the trans. 3 bolts I believe. Now, taking it off is a bit tricky. There'* a spring behind the cover. So as you back off the bolts it'* going to start coming out. Inside there is a piston with a rubber O ring. I think I would start looking there after dropping the bottom pan. Watch for any chunks in the pan.
Danthurs is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
need help! P0742 code bad00ssei Performance, Brainstorming & Tuning 23 04-08-2010 07:39 PM
Code P0742 fantastic88 1992-1999 1 01-20-2008 10:27 PM
P0742 TCC Circuit Stuck On cdt_seattle 2000-2005 8 11-08-2007 03:33 PM
TCC problem p0742 tcc stuck in locked position San Juan Cruiser 2000-2005 8 10-20-2007 01:00 PM
Transmission Trouble Kressdog 1992-1999 24 12-31-1969 08:00 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 01:54 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.