Bill Curlee

I replaced the Throttle Actuation Control (TAC) module on my 98 Coupe about 2 yrs ago and had the old one laying around. Insted of just tossing it into the trash, I preformed some surgery (actually a large hammer ) on the water tight plastic that it is sealed in. Here is what a 97-98 TAC module circuit board looks like when you take it out of the case.











If you have a 97-98 C5 and get frequent "REDUCED ENGINE POWER" issues, this module is most likley the cause. They cost $207. (Discount from $400+)

Bill Curlee

T_Vert

see no pic

dave

Bill Curlee

Try it now. It may take a little bit to down load. I attached some better pictures. The other ones were not clear.

BC

jers98vet

Great pix Bill1
Actually Fred Beans current price is $165
After reading alot of your past posts I thought it was time to finally buy one. Your posts help me out alot! Keep them coming
Jeremy

RockyL32

This piece looks like solid state electronics, Do you have any idea what on them goes out?

Bill Curlee

No, never looked into it. I do not have the schematic to do any testing or to confirm any readings! It is cheaper just to get a new one.

Bill

RoadRebel

The goofy part is why does it have a piezio electric buzzer on board..

Phil

Bill Curlee

Phil

I examined the component and it is a coil with an adjustanle slug in the center. Must be for tuning in a circuit.

Bill

Mike Mercury

Thanks Bill. The pics tell a lot.

it sounds-off everytime GM wants you to buy a new one...



really though, it that what it really is ? I've seen colis in that type package.

Mike Mercury

Damn Bill; you fast on the keyboard.

1253C5

Bill,
I had the 1998 C5 that wouldn't start, you were correct, it turened out to be the TAC module.
Question, some of these components are a little expensive. But without having one available to install and verify. It can get pretty expensive if you miss diagnois the problem. Any recommendations?

12stepvette

Nice pictures Bill.....Thanks!!! Looks like Typical Logic circuitry with an EPROM or 2 that are prone to Voltage spikes and static discharge!! How reassuring

6spd89

Here i thought the C4 Bose amp cards looked bad. I fixed the amp cards in my 89 vert,but i would not even think about trying THAT thing!!Thanks for the great pics!! BTW,where are THEY located in the C5??
Matt

DidntSettle

Gawd. I long for the days of the $5 throttle cable. I ordered up a new one for our '98. It's on the way. Thanks Bill.

Bill Curlee

1253C5

I start at the OBDII diganosis point. Examine each code and go the that area in the Service Manual. From there I read the Circuit Description, Diagnostic Aids and Test Descriptions.

For some people (this includes some GM TECHS) it is an educated guess! Its called "Easter Egging" Shove a new part in and if it doesnt fix it, go to the next big part! That gets very expensive.

If you exhaust all troubleshooting test like reading all module inputs and outputs with a meter, checking the power and grounds most times you can determine the fault. If the module is bad the proof will be seen in the testing.

Sometimes, after close examination, you will find a corroded pin, loose wire, bad plug ect ect. That will save you from purchasing a new module. There are times when you just have to just purchase and install a new module but, atleast you gave it your best shot.

Another important troubleshooting aid is understanding basic electronics and troubleshooting theroy.

I wish more people would ask how to do something than just guess. I am more than happy to explain the basic stuff like how to read a meter or or use a test light.

Bill

ericdwong

Damn electronics! I hope mine stays reliable....I love technology but at times it seems it creates more headache and more stuff to go wrong.

My bike is having issues with the speedometer right now. Its a fuel injected bike so its got a ton of sensors and wires on there. I first followed the service manual's procedure to diagnose the speed sensor. I thought it was dead, but it was not. Turns out after some fiddling, UNPLUGGING THE ECU caused the speedo to work again. Ugh, I'm gonna replce the ECU and see if that was the cause... damn electronics

Mike Mercury

Yep, and if the car is still under mfgrs warranty, GM actually forbids dealer techs from doing that type of repair (though GM is not always there to see what really goes on).

Years ago I set up a C3 module (early name for the PCM) contracted repair station for Delco Electronics. We were shipped "pulled" modules (we never seen any of the cars, as we did component level repair on the modules - and no work on the cars themselves).
We repaired about 200 computer modules per week; this was covering about a 3 state region for GMPD. We had a 40% No-Trouble-Found rate.... and that percentage was too high.

Delco was certain the modules were truly bad, and that their (our) module diagnostic procedures were faulty. They visited us almost weeky with updates to teststing software and testing procedures. Still the NTF rate remained around 40%.

Then they thought the PCM may be failing at high temperatures. So they brought us an "oven" with ports for diagnostic cables. And we would heat the modules to 80c and run the tests.
So, any that were NTF on the bench were then ran in the oven and re-tested. Maybe... MAYBE one in a hundred would fail the oven test.

Finally Delco Electronics woke-up and realized these 40% of NTF PCM's truly had no problems and they started visiting the dealers. And just like Bill states, the dealership service droids practically THREW AWAY the GM troubleshooting procedures and just started swaping modules and sensors left & right until the problem was corrected.
One dealer actually had a roll-around-cart with "one of every module and sensor". A mechanic would start swapping parts until the condition cleared. Of course only one of the replaced modules was actually faulty, but all would be sent in for repair. Hence the high NTF rate.

Another problem arose that same time... where records shown there were 3 PCM swaps on a single vehicle in as little as a month.
Again, the module repair stations were looked at under a microscope (assuming the real problem was there).

Then ... again... Delco Electronics woke-up and visited the dealer. Many times the problem was elsewhere in the car (and not the PCM moduke itself)... for example; a shorted engine idle solenoid would fry a part in the PCM that was controlling it. So when the garage droid ignored GM mandated troubleshooting procedures and carelessly plugged in another PCM... the "real" failed part would damage the replacement PCM. But the new PCM would of been clear of codes and upon startup all would "appear" to be repaired. He thought the problem was fixed.
As many of you know, CE & SES lights don't pop-on the instant something has failed... many times needing hundreds of miles driven (or hours of engine use) before the code was deemed real and the CE/SES light turned on.

The car would go back to the customer - just to see the same failure again a week later. The incappable mechanic would again swap the PCM , without bothering to pull codes and actually do any tests... and (as you have guessed) the car would come back the next week again.
What a cluster f**k.

To shorten this already long post, GM put their foot down hard and supposedly put an end to the "tube jerk" type trouble shooting techniques.
(Only you older folk that had TV's and radios using receiving tubes will know what "tube jerk" referrs to.)


If it ain't lit... jerk it out and put a in a new tube