Q: Why does my truck only change gears once while driving down the road?

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Hey I have a 2003 Chevy s10 and the transmission is acting up on it, it only changes gears once while in drive going down the road at about 45-50 then it won't shift past that it will go to 70 and then top out when it does change the gear the one time it doesn't jerk or slip a couple people told me it could be the modulator valve but idk any ideas
My car has an automatic transmission.

Hi and thank you for your question. Your transmission issue sound like that there is an electrical issue within the transmission. If you are not feeling any shifting, that is because the transmission computer unit has put the transmission into fault mode or limp mode. This will allow the transmission to start out in first gear, but it will shift directly to third gear only.

The shift packs in your transmission directs fluid through the transmission to activate the gears second and fourth. First gear and third gear does not need the shift packs. Most likely the shift solenoids have overheated and failed. Also, the throttle position sensor could cause a delayed timing of the transmission to shift.

If you do not have 2nd gear, 4th gear, or reverse, then the Sunshell inside the transmission has broken or the splines are stripped. If replacing the shift solenoids and the TPS don’t fix the issue and if the transmission has the reverse gear, then the modulator valve body (valve body assembly) needs to be replaced. If you need assistance troubleshooting this issue, a certified professional from YourMechanic can come to your car’s location to inspect the shifting problem and advise on the repair.

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