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Error code p 742

97Xcab4x4

By 97Xcab4x4
in Ask A GM Technician

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97Xcab4x4 Enthusiast

97Xcab4x4

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Can someone tell me exactly what this ( PO 742 ) code means. My tranny has an intermittent problem where the torque converter doesn't want to disengage completely. The truck will leave a stop light in low gear and immediately shift to what feels like overdrive or anything inbetween low and high? . It's like the tranny doesn't know what gear it's supposed to be in. The problem may be around for a day, or two, then go away and not show up again for weeks or months. One thing that seems to cure it is a long drive, if it's acting up, and I drive it for a while out of town, it seems to go away then. It finally sent an error code a couple of weeks ago, my buddy's scan tool came up with the 742 code. What needs to be done to permanently fix this problem? Tranny seems fine anytime other than when it has these intermittent fits. Suggestions please. Thanks

 

 

I forgot to add that this truck is a 1997 GMC extended cab with a 5.7.

Chanks7 Enthusiast

Chanks7

Posted
Posted

any other codes? p0122 p0123? Sounds like the torque converter clutch is locking up at the wrong time. Check your TP (throttle position) sensor and wiring. The TP sensor is located on top of the engine on the throttle body usually. It has 3 wires going to it, 1 gray 1 black and 1 dark blue.

 

You can monitor the TP pid with a scan tool or voltmeter. Pull up the TP pid on dataloggin or connect a digital voltmeter from TP sensor connector terminal B (BLk wire) to terminal C (DK Blue wire).

 

With ignition ON, engine stopped, the TP signal voltage should be less than 1.25V if more than 1.25V verify free throttle movement. If still more than 1.25V, replace TP sensor.

 

Also slowly fully depress and release throttle and voltage should increase to 5 volts and go vack down steadily without any spikes. If so replace TP sensor.

97Xcab4x4 Enthusiast

97Xcab4x4

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Haven't had any other codes on the truck since I've owned it. Apparently the previous owner had a EGR issue at one time or another though. Thanks for the info, I guess it's a place to start.

Chanks7 Enthusiast

Chanks7

Posted
Posted

Definitely worth looking at before digging into the tranny.

 

What kind of egr issue, the egr valve is close to the tp. Was it wiring, they probably share a ground and reference voltage wire.

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