I've searched the threads, can't find an answer.

I have a 1999 auto transmission, about 75k on it. When driving at highway speeds, using the cruise control, the cruise would disengage. I would re engage, it would disenage. I stoped using it. Then I noticed at highway speeds that the RPMs will spike about about <100k, stay that way, and then go back down. This lead me to beleive that the cruise was disengaging cause the trans was slipping. But it was so subtle that you could barley detect it at first. It only "slips" at highway speeds, and it does it more frequently if your hard on the gas pedal, being ginger with it seems to make it happen less.
Is this an actuall slipage of the trans? Is this an easy fix or the first sign of a need for a rebuild/swap? i.e $$$$$$$

Thanks

 

Cruise Control System Operation


Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades up or down may cause variations in the selected speeds. The cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, and TAP-UP or TAP-DOWN.

The main parts of the cruise control system are the Throttle Actuator Control (TAC) Module, Powertrain Control Module (PCM), cruise control function switches, cruise control brake switch, stoplamp switch, and clutch switch. The TAC module electronically controls the throttle operation under all driving conditions using inputs from the throttle position sensors, cruise control function switches, and the PCM. Cruise control related inputs to the TAC module or the PCM, other than the cruise control function switches, are likely to affect the operation of other vehicle systems. When diagnosing a cruise control malfunction, determine if any DTCs which may affect cruise control operation are stored in the PCM. Refer to Diagnostic Trouble Code (DTC) List/Type. Cruise control related inputs may be viewed with a scan tool through the PCM. Refer to Scan Tool Data List.

The Driver Information Center (DISC) will display cruise control commands when they are activated such as CRUISE SET and the selected speed, the selected speed when resumed, taped-up, or taped-down, and CRUISE DISENGAGED.The cruise control will not engage at speeds below 25 mph (40 km/h) and will automatically disengage during a traction control event. The PCM will not allow the cruise control to engage until both brake switches and the clutch switch, if equipped, have been seen since the beginning of the ignition cycle.


Please Pull & Post all your codes!

 

First, because your a new guy you should fill out your profile so people can get an idea where your from and who you are.

From your post its hard to tell what is happening. It sounds like the converter is unlocking but that shouldn't kick off the cruise. This condition happens if you hit the brakes. Make sure your brake light switch isn't out of adjustment. Have some one follow you and see if your brake lights come on. Also use the DIC and check for codes. It doesn't sound like slipage or the trans would go into safe mode and shift REAL hard by raising the line pressure.

Hope this helps.

Mike V

 

The brakes arnt setting it off. MY issiueis not whats happening ot the cruise as i think its related to what the trans is doing. Even without the cruise on its still changing RPMs under constant speeds up around 65-75 mph. There are no codes of any kind being displayed on the console.

Thanks, i'll update my profile

 

Did you try to pulling codes? If the Transmission is slipping @ those speeds the PCM should see it and set a code! There are so many things that could cause your cruise problem. It would unusual if there are no codes at all stored.


Quote:
Originally Posted by Bill Curlee
POST DTCS!!!

READING YOUR Engine Diagnostic Trouble Codes (DTC)

This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.

The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.

Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.

There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.

Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.

Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.

If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.

Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.

NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.

These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs

Here are some very good sites that explain what DTC mean:

http://www.gearchatter.com/viewtopic11755.php

http://www.obd-codes.com/trouble_cod...d-ii-codes.php

Make sure to include the H or C suffix when you post your DTCs!!

 

You haven't put on new tires have you? When I drive with my race tires on the rear once in a while it will unlock the converter. The computer senses the change and it unlocks the converter and it only happens at 70 MPH. If the rpm's only change about 500 rpm its the converter unlocking.

Mike V

 

Ok. Here are the codes. There all history as the cars been in the garage a lot recently and not driven at highway speeds


PCM-no codes
TCS- No codes
RTD- no codes
BCM- no codes
IPC- no codes
RADIO- no caodes
SDM- B1001, U1016
HAVC- B0361
LDMC- B2282, B2264, U1064
RDCM- B2283, B2285, U1064
SCM- B0851, B2860, U1255
RFA- U1255, U1096, U1064, U1016, C2115

All codes are history