New member! I've been poking around here since I bought my Bonneville, and now I gots a problem, so, first post! You guys seem well informed, hopefully I can get a little info...

I have a '95 Bonneville, naturally aspirated, 90k miles. 4T60E transmission. Here'* my dilemma:

Bought this car a few weeks ago. Drove it around, seemed ok, took it on a 300 mile trip. Car went great for about 100 miles. Then overdrive quit. I later found out that the TCC wasn't working either, but we'll get to that... After playing around, I figured it was a heat thing, and decided to check the fluid and filter. Bought a new filter and fluid, take it home, start to drain it- and it sure looks like Type F is coming out of this thing. So I get it all drained out, new filter, Dextron III back in, and suddenly the old beast is a much smoother car. Shifts into 2nd are smooth, no longer causing whiplash, ha, and overall is just smoother and most shifts are unnoticeable.

I start doing a little research, and I find out this car has a TCC. So I start checking it out- still appears that the TCC isn't working. So I pull out my scanner, and I have a code P0740. Search around, can't find any definitive info on that. So I go live info, take her for a drive and I find that the TCC solenoid is engaging. However, the converter never locks. RPM'* never drop, and the tool says it'* not engaging. When I first started looking at the problem, I thought it might be the solenoid, but that'* engaging.

I've searched around here, but I'm not entirely sure what I'm looking for at this point, I'm really little more than a back yard mechanic. What could be my problem here? What can I do to test things? Any help would be greatly appreciated. Obviously I'm buying a 15 year old car here, I'm not exactly looking to drop a ton of money at a shop

Thanks!!

SPG358 should be able to answer this one, he'* our transmission guy.

P0740 is a electrical code, which would tell me the solenoid is not working correctly. It may be getting the signal to work, but that don't mean it is.

It could be the solenoid. Don't depend upon software, your software "sees" the PCM calling for TCC lockup, but it really isn't. The PCM has no way of knowing if the solenoid is truley engaging or not.

Let'* see what SGP358 says.

Haha, looks like I'm waiting for SGP358...

I wondered if maybe the solenoid was stuck, but I've done everything I know how per my first post. Thanks for the reply'*!

*bump*
Am I in the wrong section?

I was out of town, sorry!

PO740 is usually set when the solenoid fails mechanically or when the computer sees that the solenoid was fired, but saw no RPM drop. It could also be a valve body problem, which was somewhat common. I have never seen a mechanically failed 4T60E TCC solenoid.

That'* quite alright, lol. You're not exactly my personal diagnostic technician As they say, beggars can't be choosers.

So you're thinking it'* a throttle body problem? What am I looking for? A crack? A sensor problem?

Thanks for the reply!

Edit...

Did these have the plastic body? I seem to remember something about a lousy plastic throttle body in Bonnevilles...

umm i may be missing something here but first of no throttles bodys are aluminum if i remember correctly and the throttle body it on top of the engine and also the VALVE BODY in the trans is also metal not sure if its aluminum but yeah

Since the Valve body is made of aluminum, the bore can wear out causing all kinds of issues. You will need to remove the valve body to verify IF that is the problem. It is quite an involved process to do this!