2003 Suburban LT 5.3L 4x4 210xxx miles
No check engine codes
Transmission is a 3KCD
No previous issues with transmission. Never noticed any slipping gears previously. Complete fluid change out done personally ~70k miles ago with GM fluid. Fluid still looks and smells good. Gauge cluster has transmission temp gauge and It has never overheated that I've noticed. Usually never over 150, went up to 210 a couple times when towing/country driving.
I drove ~90 minutes mostly highway with no issues doing 70mph. I arrived at a location and idled for ~30 minutes and when I was leaving the location the transmission would no longer shift higher than second gear. In drive first and second gear work fine but when it feels like it is attempting to shift into third gear it feels like neutral, the engine revs high but speed does not increase. Manually shifting into first or second works fine as well but manually shifting into third results in the same neutral feel with free revving engine and no forward power. I was able to drive off highway home in second gear keeping the rpms from getting too high.
I sourced and swapped out another 3KCD from a 2003 Tahoe that was being parted out supposedly from rusted out brake lines. I swapped this transmission with mine successfully but the same free revving neutral third gear still exists. I am not sure about the likelihood of getting another transmission with my same exact issue so I'm beginning to wonder if the issue is electrical outside of the transmission. I tested all the fuses in the engine fuse block and driver's door fuse block and didn't find any blown fuses. The replacement transmission came with the transfer case as well which I left attached when I swapped it, if that makes any difference. I dropped the pan, replaced the filter, and topped off the fluid with Valvoline Maxlife as well before testing the replacement. The new transfer case got Auto-trak II.
I will be borrowing a bidirectional scanner to see if I can read live transmission data to make sure it is actually calling for third and test the solenoids.
I read that limp mode for the transmission with force it to be third gear in "drive" and "third". How would I force it to go into limp mode?
What guidance can anyone here give me on diagnostic avenues to explore?
I am looking at possibly rebuilding the original transmission myself as well.
No check engine codes
Transmission is a 3KCD
No previous issues with transmission. Never noticed any slipping gears previously. Complete fluid change out done personally ~70k miles ago with GM fluid. Fluid still looks and smells good. Gauge cluster has transmission temp gauge and It has never overheated that I've noticed. Usually never over 150, went up to 210 a couple times when towing/country driving.
I drove ~90 minutes mostly highway with no issues doing 70mph. I arrived at a location and idled for ~30 minutes and when I was leaving the location the transmission would no longer shift higher than second gear. In drive first and second gear work fine but when it feels like it is attempting to shift into third gear it feels like neutral, the engine revs high but speed does not increase. Manually shifting into first or second works fine as well but manually shifting into third results in the same neutral feel with free revving engine and no forward power. I was able to drive off highway home in second gear keeping the rpms from getting too high.
I sourced and swapped out another 3KCD from a 2003 Tahoe that was being parted out supposedly from rusted out brake lines. I swapped this transmission with mine successfully but the same free revving neutral third gear still exists. I am not sure about the likelihood of getting another transmission with my same exact issue so I'm beginning to wonder if the issue is electrical outside of the transmission. I tested all the fuses in the engine fuse block and driver's door fuse block and didn't find any blown fuses. The replacement transmission came with the transfer case as well which I left attached when I swapped it, if that makes any difference. I dropped the pan, replaced the filter, and topped off the fluid with Valvoline Maxlife as well before testing the replacement. The new transfer case got Auto-trak II.
I will be borrowing a bidirectional scanner to see if I can read live transmission data to make sure it is actually calling for third and test the solenoids.
I read that limp mode for the transmission with force it to be third gear in "drive" and "third". How would I force it to go into limp mode?
What guidance can anyone here give me on diagnostic avenues to explore?
I am looking at possibly rebuilding the original transmission myself as well.
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