Ok about a year ago I had a tranny problem with the valve spring. I fixed it and my car drove perfect for quite sone time. Now I got a gear box fault again but when I put my obdII reader I get nothing even though it clearly shows a fault.... I once got a code but didn't write it down like a fool. My cat is shifting funking between 3-4 gear it kinda switches to 4 than shifts up and back down quickly. Any help will be appreciated thank you.

 

We need car details! See below.

If 5-spd, usual cause is 4-3 prestroke spring Sonnax - Aftermarket replacement transmission, torque converter, and high performance automotive parts and see the FAQs here

Of course, also check fluid level.

 

Be sure all electrical connectors are secure and dry.