When check engine light comes on........in my 88 Silverado K5 tranny will not downshift. It constantly shifts up to ODrive even at 5-15 mph then will not downshift unless you floor it. I like keeping it to the floor but there are times when you cant, like in town and in heavy traffic. Its driving me mad! Anyone with any suggestions post or email me. Thanks

 

That is only when the CEL comes on? That is awful strange since the transmission is not electronically controlled...

Have you tried to pull the codes? TroubleCodes.net should cover that for you.