Check Engine Light on 2001 Toyota Corolla

My Car a Toyita Allex 2001 model is showing check engine light, and whenever that happenns gear 3 does not shift to gear 4,. I have replaced the ECU and the gearbox valve body and nothing is happenning. Please help sought out this.- Peter

2 answers
Get the engine code read and post the results to further assist you. You can get a free read at an autozone or other parts store.
get a free diag from aamco