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Old 10-20-2007, 01:54 PM   #1
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Default P0742 TCC Circuit Stuck On

Hi All,

I'm starting a new thread on this subject per request. Car is a 2003 Bonneville SE (base model) with 90K miles. Symptoms include firm shifts, failure to downshift on deceleration (which then leads to lugging/chugging).

Repair shop has quoted a bit over a thousand to replace the solenoid valve. Any other parts I should get replaced while they are in there? I don't want to skimp on a $60 solenoid only to have it go next and then spend another 8 hours of labor to replace it.

Car is driven very gently overall, so I'm not looking to build a street/strip tranny or anything

Thanks!
Chris
Seattle, WA
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Old 10-21-2007, 01:35 AM   #2
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Default Re: P0742 TCC Circuit Stuck On

I took a look at the FSM (for an Impala actually, but hopefully the same) wiring diagram for the 4T65E. It looks like the pink wire provides power to the TCC solenoid as well as the 1-2 and 2-3 shift solenoids. The ECM then grounds them each through different wires, the only color I remember is the brown for the TCC.

What happens if I just cut the brown wire?

So long as the solenoid isn't shorting out somewhere before the cut (like in the valve body) I imagine this will keep it from locking and should fix the problem albeit at a loss of the locking torque convertor. Will it throw a code? I'm guessing so. Will it set the service engine light though?

Thanks
Chris
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Old 10-21-2007, 11:12 PM   #3
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Before you too far with things, try a can of SeaFoam'* Trans Tune to see if it frees things up. Run it for a few days, then drop the pan and change the fluid and filter.
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Old 10-22-2007, 03:04 AM   #4
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Quote:
Originally Posted by Archon
... try a can of SeaFoam'* Trans Tune to see if it frees things up....
Funny, I was planning on trying some kind of trans fluid fixer as well. Figure it couldn't hurt things at this point.

What'* the science behind why it may fix things up? Is there something mechanical which may just be "sticking" open/closed?

Chris
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Old 10-22-2007, 10:40 AM   #5
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There could be a build up of varnish, or other debris, on the solenoid and other parts. The Trans Tune can dissolve many of those deposits. I'm not a fan of the "mechanic in a can" type products, but experience has shown that it helps in many cases. It won't fix a failing transmission but can help extended its life.
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Old 10-22-2007, 05:48 PM   #6
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Quote:
Originally Posted by Archon
There could be a build up of varnish, or other debris, on the solenoid and other parts. The Trans Tune can dissolve many of those deposits.
I grabbed the car from the shop today, popped in some seafoam and drove around for about 10 miles but no change. How long does it normally take to clear things up? i.e. when should I move on to the next possible fix?

Chris
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Old 10-23-2007, 12:21 AM   #7
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If your fluid is in good shape, and at proper level and you don't see an improvement over the next couple of days, it would be time to move on.
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Old 10-24-2007, 01:48 AM   #8
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Quote:
Originally Posted by Archon
If your fluid is in good shape, and at proper level and you don't see an improvement over the next couple of days, it would be time to move on.
Fluid level is a bit high now with this but no improvement after ~20 miles.

I actually attempted to cut the brown wire to the solenoid. My understanding is that this would only solve the problem if the solenoid was stuck open mechanically. If it is simply shorting internally then cutting the wire wouldn't accomplish anything as the short is further up the line (towards the tranny).

The problem got better, but isn't completely gone. Still upshifts a bit early, and downshifts a bit late. The 1-2 shift is a bit jerky too.

Looks like it'* time to replace the TCC solenoid assembly. Thanks for the help thus far though!

Does anyone have a Seattle area transmission shop they recommend? I know a great one in Vanc, BC from when I lived there, but don't know any here in Seattle.

Chris
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Old 11-08-2007, 03:33 PM   #9
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The summary of this problem was I brought it in to a proper transmission repair shop and had them do the work. They listed the top failure parts for the tranny (4T65E I believe) and I got them all replaced while it was apart. This included the actual broken part, the TCC solenoid & regulator valve, as well as a new pressure switch manifold, an aftermarket fix-kit for the valve body (bore out a particular passage and install a new sleeve I believe), and possibly some other items. The price was about $800 in parts, $650 in labor.

That said, if any Canucks on the list are looking for a good transmission shop in Vancouver - ping me.

Chris
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