My Bonneville has just over 100,000 on it. A few months ago the overdrive would stop kicking in at cruising speeds. Sometimes it worked, sometimes it didn't. When this happens there is no noticeable sign other than the cel comes on and the rpms go up.

When it kicks in, the cel goes out and the rpms come back down. Now it doesnt go into overdrive at all and the cel stays on all the time. I pulled the code and it gave 39 tcc switch.

I have read several forums about the tcc switch but they all describe it as if its the tcc solenoid there will be shakes, shudders, or starting/stopping issues. I have none of the issues. The Bonneville runs fine other than my overdrive doesn't kick in.

I'm wondering if this is a bad wire issue and something else.

Any ideas?

39 clutch input circuit fault

Could be a failed solenoid. SGP358 is our trans guy here. He should have more in site on this.

if this is a failed solenoid, where do they sell them at? I didn't find a listing at the local parts store.

That would be a dealer item, or a transmission shop.

Do you know off hand what transmission you have? I thought yours was the 4t60e, but my manual says Bonneville 92-97 have that trans.

Found this.

code 39
TCC/VCC Circuit Failure Or,
No RPM Drop When TCC Is
Commanded ON

From the looks of this the TCC solenoid is commanded on, and it'* not moving. The PCM is not seeing the RPM drop it expects and is throwing the code. So to me it looks like the TCC solenoid is bad.

Ok. Thanks. Anyway to check this before taking the solenoid out?

There'* a lot of differences in transmissions depending on the type and the year. But looking at the manuals it looks like the TCC solenoid needs to be between 20 and 30 ohms at 68*f. However I can't say which pin you need to check. Some years it'* pin D, some others are pin A. Pin A is at about 5 o clock, and pin D is at about 2 o clock.

Strange... I went to town, and I don't know why, I decided to put the pedal to the floor. The tranny down shifted and the tach climbed up quickly to 6.5 before it upshifted. After I did that the overdrive kicked in and worked for the rest of my drive (about an hour).

Would it be possible that something is sticking and not allowing the tranny to go into overdrive when the TCC solenoid is telling it to?

That is possible. Have you checked your fluid level?

my fluid level looks too high. I picked up some seafoam tranny tune and a new filter and gasket.

Autozone gave me the wrong gasket/filter combo. That'* just great.