I retrieved the following troubleshooting codes from my 1992 Buick Century (V6):
26 Quad-driver sense voltage shows a low voltage when battery voltage should be present or if the sense voltage shows battery voltage when a low voltage should be present.
27 Third gear switch was closed or grounded for 10 seconds when vehicle was in 3rd gear, or drive gear was open when engine was first started.
39 TCC was commanded by the ECM when transaxle was in high gear for 15 seconds but engine speed did not indicate that the TCC was engaged.
In plain, simple English, can anyone explain what they mean?
It sounds like for some reason the tranny is not shifting when appropriate.
I really think this is one for a tranny expert. A reputable independent tranny shop should be able to diagnose the cause. Transman could give you a better reply.
Can I ask what malfunction(s) led you to read the codes?
Sometimes, when I’m in slow traffic, the check engine light flshes once or twice. That’s what led me to retrieve the engine codes.