I have an intermittent electric motor noise that seems to eminate from under or in front of the dashboard. It sounds much like that of an electric seat. It makes a humming/buzzing sound. I don't think it is the fuel pump since that is in the tank and it sounds like it is coming from behind the instrument cluster possibly near the firewall. Has anyone heard of this or have any ideas? I have no codes either or warnings either.
Thanks,
Mike

 

Could very well be the HVAC Temp Door actuators. They cycle when you first turn on the key You should NOT here it run all the time. IF SO, you have a bad actuator.

What DTCs do you see when you pull up the 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.

You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.

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!!

 

I purchased a 98 Corvette three months ago and had experienced a similar problem as you described.
Some days the noise started after a few miles intermittently and generated from the lower portion of the steering column. Therefore, the repairs bills started.
One has to start by eliminating as many items as possible causes such as ac actuators ($786.00), steering column lock bypass (159.00), fuel pumped (798.00), etc (Many $). After eliminating all those possibilities with the problem remaining, the six-way power seat had to be next. Now being out of money I removed the seat completely form the car and started checking everything out.
The problem turned out to be in the six-way seat button controller. After disassembly, corrosion was located across a few interior electrical connections. The trouble source turned out to be “corrosion” generating an intermittent ground that in turn turned on the Lumbar air pump motor. The only way corrosion could start would be by water entering this unit. With Corvette owners being passionate about their vehicles, I am betting on the cleaning of the seats as the original cause of the water intrusion. My previous owner did kept the car in a meticulous condition.
Operationally, when one presses a seat control button, that button sends a ground signal, which in turn actuates either a relay or a transistor circuit. The intermittent problem actually sent a signal to the air pump circuit that operates the Lumbers air bags and side bolsters. However, since the ground condition only turned on the air pump but not the air valve controller, only the pump ran unloaded. With no load on the pump, the category of sound and sound level was very dissimilar than any I heard before.
Oh yes, the passenger seats controller was all so removed and disassembled. Corrosion was starting in there as well.
By the way, this problem could have eliminated with a bottle of denatured alcohol and no major expense. That hurts!!!!
Hope this helps,
Bob