bigred44

1997 S-10 Pickup
4.3 L W-code engine
Engine Control Unit: #16229684

The Engine control unit is returning DTCs P0740, P0753, P0758, P0785, P1860. These codes effectively put the transmission in third gear "limp" mode. The vehicle has already been inspected by a transmission shop and has had the shift solenoids replaced as a precautionary measure. This didn't correct the problem though. I have inspected the wiring as best as I could and there do not appear to be any loose connections, broken or bare wires.

When I first start the truck and put it in drive first gear engages and the vehicle will drive normally. It will generally drive normally for a short period of time before it goes into "limp" mode. Sometimes I'll only get a half mile and it will go into limp mode, other times it will drive longer distances, 80+ miles without any problems.

After its in "limp" mode, if you stop, turn off the engine, wait a minute or so and then restart and drive it you have all the gears again.

Does this sound like an issue with the Engine Control Unit? Or would an issue with the Engine control unit be more patterned? (I.E. would it would always go into limp mode quickly).

servtech009

I have a 97 s1o with what appears to be the same problem. I get an ses light and when I pull the code it says trans component slipping. The transmission only acts up after driving on the highway for a while and it only seems to have trouble with the first 2 shifts. would like to know if this is a major or minor problem. any info will help

blazee

Your problem is caused by a lack of power to the transmission. The most likely culprit is the ignition switch.

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blazee

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blazee

Was the code P1870? Your problem is probably the valve body.

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bigred44

After testing for power at the transmission fuse I found that I was only getting power to this circuit about 50% of the time. I replaced the ignition switch and its been working great ever since.

Thanks for the help!

blazee

You're welcome. I'm glad to hear it's working again.

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