# obd1 trouble codes, 42,74,85,86



## bassfishn1 (Jan 14, 2008)

been having an issue again with this tranny acting funny sometimes, getting stuck in 2nd, not downshifting, gear slamming,etc. got in the truck today and drove for a few miles and truck started running rough, and check engine light came on, got home and puled the codes. i got 42,74,85,86, iread the definitions, but can't seem to put it all together
can anyone help?, pls. thank you
94'chevy k3500 5'7 4l80e


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## B&B (Nov 4, 2006)

One of two _general_ common denominators here with this list of codes.

Either the ECM has an intermittent ground issue, which means its time to go over ALL the ground wires/connections under the hood. Or you have an issue with the vehicle speed sensor (or input sensor) or their related wiring. Need to do some investigating...

Check the harness coming off the speed sensor in the T-case tail-housing as well as the connecting plug itself. Also check the input sensor in the side of the trans..located just above the shifter linkage.

Check the cab to engine as well as the battery to frame grounds. There's also a ground on one of the thermostat housing bolts..this is a secondary ECM ground...make sure it's sparkling clean and tight.

A scanner would help narrow this down some.


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## bassfishn1 (Jan 14, 2008)

ok, tnx b&b, now where to get a scanner? do u mean a tranny scanner? damn, i feel dumb


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## B&B (Nov 4, 2006)

bassfishn1;596869 said:


> ok, tnx b&b, now where to get a scanner? do u mean a tranny scanner? damn, i feel dumb


You need a good diagnostics scanner like a trans or general repair shop would use...an OTC or Snap-on for example. If you've got any friends in the repair business thats where you want to go.


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## bassfishn1 (Jan 14, 2008)

ok, tnx again for your help, will check this out


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