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P0742 Torque converter clutch circuit stuck on

11-12-2005, 08:55 PM
I have '98 Pontiac Grand Prix GTP Supercharger 3.8L. This week the check engine light came on and car would buck like a horse when accelerating after a stop. Not always...but sometimes. Got the codes, there were three of them.

-#3 cylinder mis-fire
-#3 fuel injector
-Torque converter clutch circuit stuck on

I fixed the first two, new spark plugs, new wires, new #3 fuel injector. Not sure what to do about the other one or if it was still a problem so I reset the light. Drove around all day, no problems. My wife gets in and goes to the store and same thing happens, check engine light came on and car bucked like a horse when accelerating after a stop.

A friend told me that it could be the tranny starting to have problems - someone else said changing the tranny fluid and filter might fix it. Guy at Autozone said my engine mounts might need replacing and this might be causing the problem..I saw in another post that it might help to put in some Sea Foam or Lubeguard? I don't know what to try or do first! I'm told that front engine mounts are dealer items and the bottom 2 are approx. $100 Could motor mounts actually cause the TCC to stick in the on position? The motor does move some when I shift from Park to Reverse to Drive, etc...but how can I tell if mounts are really bad? Don't want to replace them only to have the same problem. Are there any other things that could cause this that I might be missing?

Thanks for any help at all!

11-13-2005, 12:49 AM
I don't think the motor mounts are the reason why you have a tranny error code. With the torque convertor clutch stuck on, the torque convertor is not disengaging causing the bucking. There is a constant TCC apply. It means you probably have a defective TCC solenoid or TCC-PWM solenoid on the valve body. To correct the problem one of them needs to be replaced.

On the driver's side of the tranny (top) is the 20 way electrical connector. Disconnect it and then re-seat it.

In the interim, you have nothing to lose by putting in an additive such as Sea Foam or Lubegard. Under $10.00 cost. It may help unstick the stuck TCC valve. The stuff works wonders on minor valve body problems. Good luck!

Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

11-13-2005, 10:14 AM
A P0742 is usually caused by a hydraulic or internal transmission concern.
The TCC release switch is a normally-closed switch and anything that can cause it to stick open will cause this code.
Inspect theTFP manual valve position switch.
Inspect the TCC release switch for the following conditions:
- A damaged or leaking seal

- Sediment or debris

- Damaged switch contacts

- Stuck switch contacts
TCC control valve stuck

- TCC feed limit valve stuck

- TCC regulator apply valve stuck

- TCC PWM solenoid valve stuck

- Pressure regulator valve stuck

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