msu-dawg

So I'm driving down the highway today when all of a sudden the car starts slowing down and I'm getting lights on the dash and messages on the DIC. I had been running with the cruise control on about 75 or so when this happened.

The "check engine" light was on as well as the traction control light. I eased over to the side of the road and left the car idling. Seemed to be idling rough. It was yelling Reduced Power, as well as some sort of Traction Control error. I found this all very odd as to what caused those two seemingly unrelated problems without warning.

With the car still running (at a strange feeling rough, low idle I might say) I sent into diagnostics and found a P1518 and a code in Traction Control that I don't remember off the top of my head. As soon as I cleared the P1518 the idle came back up to a normal level. The TCS DTC came right back when I tried to clear it.

So I do a quick search on the TCS DTC on my blackberry and discover that it appears to be related to disabling of the TCS by the PCM when certain PCM problems occur. So I shut the car off, pull key, then restart. The TCS problem is gone (or at least stayed gone when cleared, can't remember which). I decided to not worry about that presuming it's simply a side-effect of the P1518.

So I searched the P1518 quickly and find that it's related to Throttle Actuator Control. So, with the car in park I revved the engine a bit- so as to make the throttle actuator move. No problems appeared so I waited for a long gap and pulled back out in traffic.

Drove the car a bit around town including 2 stops- first the car sat for about 2 hours and 2nd for about 15 minutes or less. Restarted and ran fine both times.

So I have a lot of research I can do but I wanted to ask if anyone had any suggestions about particularly good threads to read on this issue. Also if you think this might be a random isolated incident or if I should view it as a prelude of more problems to come?

Bill Curlee

BEEN IN YOUR SHOES! My 98 Coupe did the same thing.

97 & Early 98's had an issue with the TAC Module (Throttle Actuation Control) Theres a TSB on the issue. I replaced mine and no longer had the issue.

You can also have an issue with:

-The Throttle Position Sensor

- Accelerator Sensor

-wiring/connectors
-Throttle body drive motor

If I were you, I would just clear the DTCs and monitor. You already know that you can clear the DTC and GO>>>>>

BC

Sebring97C5

Sorry If I don't remember all the specifics?

I had the same problem 5 years back and I was getting the reduced power/service traction control.
This was a random and recurring issue for several months. I was finally able to isolate the cause to a faulty sensor in the gas pedal. I replaced the entire gas pedal (only option) and I have had no issues since.

This was my experience. I hope you can successfully isolate your problem.

msu-dawg

Thanks for the replies fellas. Sounds like maybe I should expect the gremlin to reappear.

I have to say it was a little disconcerting. That was my first experience with reduced power and BOY DO THEY MEAN REDUCED!. I didn't put the pedal to the floor or anything but I did tip my foot into it quite a bit and the car basically felt like it was just dead. It appeared to have no intention of remaining at highway speed. Is this normal for Reduced Power mode?

I forgot to mention but the car is a 98 coupe, although I don't remember how early in the production year run.

I've dealt with the faulty oil pressure sender, dim climate control display, column lock fiasco, rocking seats, and sticking window motor/regulator. I suppose I'll deal with this too!

DeeGee

I had a random reduced power incident in Vegas in 2005. Same as you and the car just coasted to a halt. It never reoccurred and I still have no idea why it happened. I didn't pull the codes at the time so can't add to your diagnosis. The only thing I can think is that the OEM battery died shortly afterwards and may have had something to do with it.

msu-dawg

Although I can't say for sure, I seem to recall that the issue occurred just as I had bumped the SET/COAST button on the cruise control. I'm not sure if this is purely coincidental or not.

Based on the schematics I've looked at the signals from the cruise switch & buttons go into the TAC. This obviously makes sense since with DBW there is no additional throttle actuation device and the TAC provides the signal to the servo-motor that actuates the throttle plate.

Based on either specific knowledge/logic, or purely intuition, does anyone think that the input from the CC stalk could have triggered some strange happening in the TAC? Or is it most likely an issue with either the TAC itself, the feedback from the TPS, the input from the APP or a wiring/harness issue?

Guess I'll plan to drive the car as I normally would and just be on alert for a problem. If it happens in rush-hour traffic though that's really gonna suck.

Bill Curlee

Document ID# 410906
1997 Chevrolet Corvette


--------------------------------------------------------------------------------


Subject: REDUCED ENG. POW. MESSAGE ALONG W/ PARTIC. PWRTRAIN, DTCs P1516, P1518 and/or P1125 #87-65-16 - (03/24/1998)


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

FIGURES: 00 ATTACHMENTS: 00

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.

COPYRIGHT 1998. GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.




new udated part #
12578953.

Any 1999 + TAC Module can reliabley replace a defected 1997-1998 TAC. Inspect all the throttle by wire components and wiring and if its all good, you may need a TAC module.

SUPERCRUZ

Hope your TAC does not fail and leave you stranded. My TAC failure also burn up my PCM. My car spent several months in the shop until the TAC was unltimately found to be the culprit. in addtion to a P1518, I also had a P0606. I would go ahead and pony up the $200+ for a new TAC. It is not all that labor intensive to install at a qualified shop and you will have piece of mind. Good luck with it.

Bill Curlee

If you decide to get a new TAC module,,, Gene Culley www.gmpartshouse.com has the best price I found when I purchased mine!

msu-dawg

Thanks for info. I've bought several items from Gene, the most recent being new TPMS sensors. And I had already looked up the price of the TAC from gmpartshouse.

Bill Curlee

My 98 TAC module got so bad, I was afraid to drive my car further than I could walk home!

After messig with it, I found out that I could pull up the DTCs in the DIC and clear the DTC and it would run normal fo a while. I got real good at doing it.

TAC module replacement CURED it 100%

BC

c5blo

Ha Ha ! I feel your pain... I walked home last night

BigStig

I'm still sweaty and pissed from a long walk home..
Did you ever resolve your issue? Do you remember what it was?

I've been having gremlins here and there, but I was just haulin-a down the highway, hit my left turn indicator and *poof!* All electrical and engine was just gone.
Made it to the shoulder, sat there a minute, made sure everything was off and restarted.. it stumbled and spat, gave a low power warning then shut off. Sat a few more minutes, tried it again, started up like there was never anything wrong.
Darted across the highway and mashed the throttle to get as much momentum going as I could.. because my mechanics shop is just down the hill.. got to the first light, turned red.. on green gave it throttle, sputtered and died. Went through the whole routine again.
Made it to the mechanics shop.. pulled in, he came to my window and I described what happened, car still idling.. he looked at me like I was crazy. I hit the left indicator.. nothing, right indicator, nothing! "I swear it just shut off when I used my indicator."
Couldn't have planned this better, he said, "well there's nothin that should make it shut off by just using your turn signal.." as he reached in my open window and lifted up on the turn stalk.. *Poof!*
finally it does it in front of the mechanic! We messed around with it and it finally threw a code.. p1518.

So.. from my forum searches it could be anything from a #17 fuse not getting it's 12v with the key on, the throttle actuator.. or the throttle peddle?

(And yes, I realize I'm necro'ing this thread (bringing it back from the dead) but I'm hoping you're still around.)

Bill Curlee

All of the ABOVE stated information and,,,,, You still did NOT provide any DTCs!

The LACK of DTCs or ONE DTC could point one of us in the needed direction of providing you the necessary steps to solve this issue.

STEP 1 CLEAR ALL your DTCs.
STEP 2 The very next time this happens,,,,,,,,,,,,,,, WITHOUT turning off the IGNITION,,,,,,,,,,,, READ the DTCs and post what you find (ALL OF THEM) and include the H & OR C

There are TOO many things that can cause the same symptoms.

Bill

msu-dawg

As I recall, I had this reduced power thing happen one additional time after my initial post. It occurred right after I had stopped at the guard station to show my badge on the way into work on a military base. When I pulled away I got the reduced power message so I immediately pulled to the side, cleared the code, and then pulled back into traffic. I don't think this issue ever occurred again and I definitely have not replaced the TAC.

No complaints from me... no reason not to post to an old thread if it's applicable to what you're digging into!

BigStig

OK, I've sent over the DTC pdf to my mechanic. We both thought that a code scanner (p1518 fault) would provide more info than the cockpit display.
I shall report back with our findings.

Bill Curlee

DTC P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit

The TAC module has to have serial data. If that is the only DTC that you have, you need to do a couple of things:

1- Check fuse power to that module When the key is ON, you should have FULL BATTERY on the fuse test points.

2. Module Ground You already checked the grounds.

3. May have a bad TAC Module.

Bill

BigStig

Two mechanics later.. it was the Ignition.
Car runs perfect now *knocks on plastic*

BLUICIDE

When you say "ignition", do you mean you cleaned the contacts within the ignition switch? Figure that's where I'll start b4 buying new parts. 98 Cpe w/ LS3 implant makes it kinda tricky. Thanks.