qwck10th

Hi fellas, car details are in the sig. I've been searching and reading but can't find a clear path to vette nirvana - at least not a path that I like.

DIC messages: Reduced Engine Power, Service Traction System, and Service Active Handling.
DTCs:
P1518 PCM to TAC Module Serial Data Circuit,
C1278 TCS Temporarily Inhibited By PCM, and
B2597 Traction Control System Switch Circuit. All Current codes. No other codes.

History: codes started (on start-up) last Fall, got too busy to chase them and parked it for the winter (batt disconnected, Battery Tender attached.)
This Spring, jump in to pull the codes and everything is fine only the B2597 is Current. (huh?). Drive it a couple days no symptoms. Park it a couple days and symptoms/codes
are back to stay (ugh!)

The C1278, I'm ignoring, figure it is caused by P1518. The TC switch could be causing the P1518 TAC issue, but seems unlikely (correct?)
Have a new-to-me switch coming from eBay. If that fixes everything, I'll be shocked, and relieved

Assuming the new switch does not fix the P1518...
The battery is good: a new DieHard sitting at 12.4v - stays on a trickle charger.
Car starts, codes/symptoms occur immediately, will not clear. Engine starts dropping cylinders (REP mode kicking-in, I guess.)
I've tried disconx the battery and waiting - no joy.
Checked and reseated the TAC connectors - they were perfect.
Checked and reseated the PCM connectors while I was there - they look perfect.
Fuse 17 has B+ with the key on. Zero v with the key off. Fuse is good.
With key-off, throttle plate moves (by hand) from closed to full-open with some slight resistence - feels like a stepper motor, no binding or grinding.
The motor makes a soft whirring sound as it moves. If held wide open and released, the throttle plate does not "snap shut", but closes quickly with a slight bounce at full close.
When the key is turned on (not started) throttle body flicks opens slighly (about 1/2 inch), then returns to near closed and stays there.
When the key goes off, it appears to close completely.
The plate does not feel super solid on the cross bar (I'll check that.) Light oily/carbon residue behind the plate (a different topic.)

So, the parts in this circuit are not cheap (at least not to me.) $400 for a TAC module! The other pieces (APPS, harness, TPS, TAC motor/TB) I'm hoping they are okay as I have no other codes. And, I've read of others throwing parts at a P1518 without success.

I do not have the Factory Service Manuals, and I'm not sure they help much unless I have a Tech II on-hand. It's just me and my multimeter.

Questions:
1) I have access to HPTuner can it give me more insight and point me to the offending part? Can a Tech II do that? Seems like I've read about people getting more diagnostic info than just the DTCs.
2) Ignition Switch??? (seems like I'd have low voltage at Fuse 17)
3) Should I make a donation to the local church, put on my big-boy pants, start buying parts, and pray I get the right one the first time?
4) Any suggestions for a path the vette nirvana?

Thanks in advance,
Steve C.
2000 vert, z51. CLB, CAGS delete, shifter.

qwck10th

I had already ordered a new TC switch. Installed it. The TAC error went away, but the TC switch error stayed. Drove the car, it was fine, except for the TC switch doing nothing. Parked it for an hour, restarted it and the TAC errors are back; TC switch error too. Sigh. A comedy of error (codes.)
s

qwck10th

Some updates for future sufferers of P1518. Short version, no joy yet.

Cleaned the batt- connection. Found some light corrosion, but no change to the symptoms.

Checked the BCM connections. No changes.

I wondered if my symptoms might be a bad ignition switch. So, checked the fuses recommend by Bill Curlee in his stickied thread. I show some slight voltage drop, but nothing dramatic. Those numbers are below:
Batt, key off, door closed 12.37
With Ignition On. Battery: 12.28
Eng Ing1 Fuse 19 12.30
Injr 2 Fuse 18 12.27
Throtcont Fuse 17 12.27
Injr 1 Fuse 22 12.25
PCM Fuse 16 12.17
F/PmP Fuse 13 12.14

I did not check the Instrument panel fuse block, ran out of time. But, 21, 22, and 19 need to be checked there.

A couple of test drives around the block left me limping home at 2mph (grrrr ) This was the first time it had failed while on the road. All other failures were intermittent, and immediately post start-up if they were going to occur - otherwise it would start, run, and restart flawlessly. Tried starting it a couple more times this morning to see if I could get a new code to give me a clue. Only the P1518, and B2597 showed Current. Interestingly, during a normal start-up (no CEL, no Reduced Engine Power...) the motor was idling normally, then idled up to 1500 RPM and stayed there all by itself - I was not touching the throttle. Then the DIC lit-up, the bells clanged, and the codes and messages returned. That sounds like garbage signals being sent to the TB.

I haven't decided if it'll be cheaper to take it to a shop (LSXperts, and Vengance are nearby), or start throwing parts at it. This sucks - as y'all already know.

More updates to follow. I'm going to find the problem, put my foot on it's neck, and kill it. Then I'll have a cold one.

Steve C.

Ronnie_W

What was the result in the end?

Brackets

This member hasn't been here for nearly three years.

Ronnie_W

The cause of the problem is still the same. Time does not change that!