Obd2 code p0740 -- torque converter clutch circuit open
My Tahoe has had this error code ever since we had it rebuilt this past summer (2012). I pulled and installed the tranny myself to save on money, as my father-in-law has numerous connections when it comes to parts and repairs. Aside from minor damage to a port on the neutral safety switch (pnp switch), the install was uneventful. I've since replaced the switch so the plug fits nice and snug. I've read and erased the code numerous times to no avail, hoping that it was an old code stored from before the rebuild. It should be noted also that we replaced a faulty catalytic converter including the entire y-pipe prior to the transmission malfunctioning. As a matter of fact, I believe the faulty cat led to the transmission problem although I'm not sure. Anyways, I've read this ident and troubleshoot page here:
It says that in some cases, there may be performance problems, such as dying when coming to a stop after driving on the freeway and/or misfire-like symptoms.
This has happened two or three times at (unbelievably) the same stop light on the far side of a freeway overpass. It also says in unusual cases, there are no adverse conditions noticed by the driver. Aside from the few times its died, it shifts regularly, on time, and seemingly with the proper rpm drop with a steady acceleration, including overdrive. Also, when I press the brake, there is a noticeable click from under the dash. I've heard that a brake switch may be the culprit and am curious if a click is good or bad :)
The code reader we bought from harbor freight doesn't include the freeze frame data needed for further diagnosis, and I'm wondering if there are any glaring problems I should be aware of before we take it to the Aamco up the street. I'm fairly handy and aside from pulling apart the tranny itself, I'm hopeful that there may be a fix for this or at least a better direction to face or some kind of information I can arm myself with when taking our to the shop in that scenario. Please help.
When I mentioned it dying at that stop light, I hadn't been on the freeway. I had, each time, driven about the same distance that the transmission reaches operating temp. I think a mile or so from the house. I'm assuming the operating temp because my other car kicks into overdrive after a high rev at about the same spot each morning.
December, 3, 2012 AT 12:40 AM
These trucks have a super high rate of ignition switch failures causeing tranny problems and/or tranny codes. Do to low voltage. Based on that fact alone I would suggest that you start there. You are pretty handy so I assume that you own a multimeter. And know how to use it? Ok the first thing you do is with the truck running check to see what the charging voltage is at the battery( I think around 13.9 or so) mark that voltage down. Now with the vehicle still running locate fuse that is labeled the " ign o" fuse in the interior fuse box(at drivers side end of dash I think) and check voltage across both terminals of that fuse just like you did at the battery and mark it down. If it is less than what you had at the battery, then now access the white wire at the ignition switch, if it has less voltage than you had at the battery then replace the ignition switch and clear your codes.I really think this is where your problem lies, i've done to many to count. And the code was probably there before you pulled the tranny i'll bet. Please let me know what you find out. Thanks for choosing 2carpros.
December, 9, 2012 AT 8:41 PM
I really appreciate your help on this thanks for all your input: ) I finally got a chance to check the voltage across the points you mentioned today. I'm showing the same voltage across the battery, fuse and white wire on the ignition switch. 14.2V. I assume this means the switch is ok. In your experience, might there be any other factors or culprits involved? Again, thank you, look forward to hearing from you.
December, 10, 2012 AT 1:17 AM
Good job justin and you are very welcome. Anytime. At this point I think you may be better off to take it to a tranny shop for diagnosis. Shouldn't be more than an hour labor. But at this point the testing to the bcm, tcm, ect becomes very specific and tedious and I really think that you best bet is to take it to a tranny shop. Thanks for your kind words and thanks for choosing 2carpros.