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Q: How can I tell if it's the throttle body or the transmission at fault?

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while on the freeway i was trying to accelerate and it wouldn't. i got the throttle body cleaned. I've noticed before and after the shifts a little rough, meaning it jerks when shifting gears. i haven't noticed any burning smells, slipping of the gears or any grinding noises when the gear shifts. the rpm doesn't change too much. i have gotten the codes read when the check engine light comes on and it gives transmission and throttle body codes. i don't want to spend the money on another transmission if i don't have to.

My car has 130000 miles.
My car has an automatic transmission.

A: Hi and thanks for contacting YourMechanic. ...

Hi and thanks for contacting YourMechanic. Check the fluid to the transmission, and look at the color of the transmission oil and see if it is red or dark red. If it is dark red (varnished), then change the oil and filter on the transmission. This can correct most shift issues. If you still continue to have harsh shifting, then either the transmission control (valve body) has a stuck valve or the accumulator has a broken spring and needs checking.

If you need further assistance diagnosing your vehicle, then seek out a professional, such as one from YourMechanic, who can come to your location to determine why the car is shifting hard and perform any needed repairs.

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