P0785

[Darbycrash]

1997 blazer 4x4, I am getting the infamous code when engine is warm I will get a CEL and at the next stop light no more 1st or drive gears......I think I have it narrowed down to 4 things also remember the truck runs like a champ until it warms up.... The first most popular thing is the ignition switch (I do have other existing issues with power including: no blinkers, faulty gas gauge, faulty 4wd, and sometimes when I get in and shut the door all the power from the battery goes offline as is there were no juice. If I re- slam the door it will usually comes back on.(This is a less common fault but does happen)
2nd is the vehicles computing system sending a faulty message to the transes timing solenoids. 3rd would be the solenoids themselfs. And my. 4th speculation is since it happens when the truck is up to normal operating temp is a mechanicle part in the valve body getting warped and expandind causing it to hang up on something this not allowing downshift to first or upshift to drive above 50 mph. As you can see replacing all of these things would be costly and not worth my time. I have seen numerous posts with the EXACT same problem but no sucsesfull follow ups on what acually fixed the issue. any help would be greatly usefull! Also please excuse my spelling.... Thanks guys

[MT-2500]

Originally Posted by Darbycrash

1997 blazer 4x4, I am getting the infamous code when engine is warm I will get a CEL and at the next stop light no more 1st or drive gears......I think I have it narrowed down to 4 things also remember the truck runs like a champ until it warms up.... The first most popular thing is the ignition switch (I do have other existing issues with power including: no blinkers, faulty gas gauge, faulty 4wd, and sometimes when I get in and shut the door all the power from the battery goes offline as is there were no juice. If I re- slam the door it will usually comes back on.(This is a less common fault but does happen)
2nd is the vehicles computing system sending a faulty message to the transes timing solenoids. 3rd would be the solenoids themselfs. And my. 4th speculation is since it happens when the truck is up to normal operating temp is a mechanicle part in the valve body getting warped and expandind causing it to hang up on something this not allowing downshift to first or upshift to drive above 50 mph. As you can see replacing all of these things would be costly and not worth my time. I have seen numerous posts with the EXACT same problem but no sucsesfull follow ups on what acually fixed the issue. any help would be greatly usefull! Also please excuse my spelling.... Thanks guys

Welcome to Af.
You are 12 volt losing power or connection someplace.
Start with ign switch and fuse box.
Get a good wiring diagram.
Check for lose of 12 volt ign and 12 volt battery power.
Remember 97 is a bad year for ign switches.

[mike2004tct]

You definately need a new iginition switch module harness, ~$125.00 at Autozone or similar type of store.
I never got a code when my switch failed, but others have, and you have all the symptoms of a bad switch.

The warmed up bad operation is another thing, though, and most likely not related to the switch.