Help! '98 has been at dealer since late March; reduced engine power. Part on order and due in July!??? Parts Manager states there are none anywhere so it's coming from the factory. I've checked online and found none. Would like to have the car running before husband returns from Afghanistan on leave; he has not seen his new baby yet. Any suggestions?

 

What was the malfunction and did you pull the codes? I'm guessing you didn't pull the codes but if you can, go to the dealer and ask them to do so. I can only remember hearing of a single TCS failure here that wasn't the pedal itself.

 

The 97 & 98 C5 did have a corrupted TAC module issue. My 98 had a defective TAC but it was repaired by replacing the old module. It can be replaced by any TAC 1999+ NEW TAC-MODULE PART # 25319443

Check the part number on your module and se what it is. Tac modules do go bad, so even if its a 99+ module, it might just need a new one.

Have you checked with Gene Culley www.gmpartshouse.com for part availability??? If anybody can get one, they can.


So,,, what are they going to do if the New TAC Module doesn’t fix the issue??? There are NUMEROUS things that can cause REDUCED ENGINE POWER and there all Throttle By Wire circuit issues.

Just like "dgrant3830" recommended, having the specific DTCs will help pin point the issue and to help make sure that there really on the right track and not chasing ghost!

There was a TSB that detailed specific DTCs and symptoms of the bad TAC Module. I will see if I can find it. A Technical Service Bulletin (TSB) is NOT a recall so dont think it giong to help you with a free repair. It just alerts the Tech about a specific New Known issue and the proper way to correct it.

Whoops, there it is...
REDUCED ENG. POW. MESSAGE ALONG W/ PARTIC. PWRTRAIN #87-65-16
SUBJECT: REDUCED ENGINE POWER MESSAGE ALONG WITH PARTICULAR POWERTRAIN TROUBLE CODES (INSTALL NEW TAC-MODULE IF STRATEGY IN SERVICE MANUAL FAILS)

MODELS: 1997-98 CHEVROLET CORVETTE WITH 5.7L V8 ENGINE (VIN G - RPO LS1)

CONDITION #1: INTERMITTENT REDUCED ENGINE POWER EVENT, ACCOMPANIED BY P-1516, OR P1518 TROUBLE CODES.

IF A SITUATION ARISES WHERE A P-1516 TROUBLE CODE IS ACCOMPANIED BY A

P-1120 AND/OR P-1220 TROUBLE CODE, THIS SERVICE BULLETIN DOES NOT ----------------------------------------------------------------- APPLY. IN THESE CASES THE TECHNICIAN MUST USE THE NORMAL STRATEGY ------------------------------------------------------------------ BASED DIAGNOSTIC. -----------------

CONDITION #2: INTERMITTENT REDUCED ENGINE POWER ACCOMPANIED BY TROUBLE CODE P-1125 AND ANY OF THE FOLLOWING TROUBLE CODES:

P-1276 P-1281 P-1286

CAUSE:

CONDITION MAY BE DUE TO DIAGNOSTIC SOFTWARE AND CALIBRATION IN THE TAC-MODULE WERE NOT OPTIMALLY UTILIZED.

CORRECTION:

IF THE ABOVE CONDITIONS CANNOT BE CORRECTED USING THE NORMAL STRATEGY BASED DIAGNOSTICS LISTED IN THE SERVICE MANUAL, INSTALL THE NEW TAC- MODULE LISTED BELOW.

PART INFORMATION:

NEW TAC-MODULE PART # 25319443

PARTS ARE EXPECTED TO BE AVAILABLE ON APRIL 6, 1998 FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION: J-5582 LABOR TIME: 0.5 HR


When my car would go into reduced Power, i could clear the PCM DTCs on the fly and the car would continue to run normally. I got very good at it and could pull up the Diagnostics, clear the DTC and be back cruising in less than 30 seconds!

My new TAC module FIXED my issue.

PS:
TELL YOUR HUSBAND,,, “THANK YOU FOR SERVING!”

 

Ya know,,,,,,,,,,,, If it were me,,, I would go to that STEALERSHIP and have them plug that module back in and see if the car is still in REDUCED ENGINE POWER (REP) Mode!!!!! If it is, clear the DTCs and see if the R.E.P. will clear and the car will run normaly.

2. If the car has been there for a FRIGGEN MONTH!!!, The batter is going to need to be charged!!! So, make them do that.

3. Where is your car being storred???? INSIDE or OUTSIDE???

Here is how you can read and clear your own DTC from inside the cars:

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!!
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WOW! Your going to know MORE about this car than your hubby will!!

Im going to PM you my cell number. If I can help,, call me!

Bill Curlee

 

The codes we pulled off the car in March were 0654, 1518 and 1571. The dealer plugged in and pulled the bad throttle mod code and placed the part on order. Prior to going into the shop, a friend pulled the PCM and cleaned all the connections - still no go so off she went to the dealer.

 

P0654 Engine Speed Output Circuit
P1518 PCM to TAC Module Serial Data Circuit
P1571 ASR Desired Torque