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Overdrive issues

by Scott Pyle
(Springfield mo)

I have a stock 99 auto 4l60e. I just had it rebuilt so the tranny is fresh but I still encounter an issue with it staying in overdrive. The cruise control acts up at the same time along with the tranny temp. But the main issue is the O/D. It's killing my mpg. It will sometimes not work at all and other times it wil obviously float into and out of o/d. How does the electronics play a part in this situation? And is the electronics the problem. Also a side note I do have after market wheels that are 335/35/18 is that a problem that can be corrected without getting rid of the wheels if it is a part or the whole problem?

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Oct 23, 2011
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Your overdrive problem
by: Corvette-web-central

Hold the phone I think I have found your problem! Under the dash is the brake light switch and a TCC (Torque Converter Clutch) Brake switch on the automatic transmission or its called the Cruise Control Brake Switch in the Manual Transmission cars. This switch disengages the cruise control but also disengages the torque converter clutch upon brake pedal movement. It will not set the Malfunction Indicator Lamp but it will set code P0571.

My theory is that the switch is defective, maladjusted or has debris affecting normal operation. I m almost positive this is your problem and suggest going to this switch first!

Just remember these are probably 2 different switches on the brake pedal. Brake lights and your cruise control TCC switch. A third switch is located at the extended travel position when your brake pedal goes all the way to the floor. I just went and looked at our C5 and cant tell for sure the number of switches so I m just working off our manual. I will keep researching and try to get you more info.

Please post the codes when you get them! I m interested to see if they are the same!
Thanks,
Chris

Oct 23, 2011
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Overdrive issues
by: Anonymous

Yes it did have the issue before the rebuild. Also how hard is it to find and fix a knock sensor? Also how do I find out if it's the knock sensor. I don't have any codes that says anything about a knock sensor. But I do have some codes and will post them

Oct 09, 2011
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Knock Sensors
by: Corvette-web-central

Not sure if you have any engine codes but it may not hurt to look. Directions here: http://www.corvette-web-central.com/C5DTCcode.html If you find any codes write them down or take a picture of each one then come back here and post. Its possible that the knock sensors may have a problem or you have an engine problem causing knock. Every time the engine senses knock it will disengage overdrive to remove the load from the engine. Your tires are only .5 of an inch different in size larger so we dont suspect them as the cause.
A few questions?
1.Did it do this problem before the rebuild?
2.You state its stock but sometimes a change in camshafts can cause a problem with the knock sensor system?

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