A good friend of mine and fellow track rat has a really big problem with his 2002 C5Z06. I’m starting this thread to chronicle our diagnosis and repair. If you have any insight, please chime in. The car will be at my place this coming Wednesday to start (hopefully) correcting his problem.

Background: 2002 C5Z06, approx. 10k miles, 2k of those HPDE miles. Car tastefully modified approx. 5 yrs ago. Approx. 50 track days on mods, advanced level driver. 1 yr. ago, crash on track with impact at RF fender PCM area. Car repaired at body shop, dealership replaced PCM. Tuner re-tuned new PCM (speed-density, same as tune done 5 yrs ago). First track day after repairs, car ran great for 2 sessions, then went into limp mode. DIC Displays: Service Column Lock, and Reduced Engine Power. Owner indicates an LMC5 Column Lock Bypass is installed.

Initial Diagnosis: DTC Codes: P0103H/C, P1120H/C, P1220H/C, P1514H/C, P1515H/C, P1516H/C, C1278H/C. The P0103 is due to the speed-density tune. Scan Tool KOEO: All 3APP sensors show correlation through 0 to 100% pedal position, TP sensors showing correlation. However, TP does not change with increasing pedal position. Physically pushing open TB, scan tool shows TP sensors change both voltage and % with no correlation errors. Scan tool shows comm with PCM is OK. Note: KOEO test on known good 2002 C5Z06 shows that TB does move with increasing accelerator pedal. So my conclusion from initial diagnosis is that the APP sensor and the TPS are both OK even though the P1120 and P1220 codes suggest the TPS could be bad. I confirmed with a multi-meter that all APP and TPS 5V, low reference, and signal V’s were the same as shown by the scan tool. Clearing Codes, upon KOeR, codes re-appear after about 2 seconds. Suspect possible bad TAC.

Visual Inspection: RF tire and rear inner liner removed to expose TAC module and PCM. This revealed the dealership left the PCM mounting bracket in a broken state (broken during the crash). This allowed the TAC module to flop around. Further, it was necessary for them to disconnect the PCM and TAC connectors to replace the PCM. The gray protectors over the PCM wires were loose and the locking tabs broken. Now for the big observation. The 16 pin TAC connector, C2, was distorted and upon removal it was found that the translucent-gray connector guide was missing, so the connector female contacts were free to flop around. I’m hopeful that this may be the cause (connector contacts not making good contact with module pins combined with the TAC flopping). I couldn’t do anything about that at his house, being 3 ½ hours away. I was amazed that the dealership missed an opportunity to GOUGE a customer for many more parts and hours, some ACTUALLY needed.

Initial Conclusion: I’m hopeful that replacing the C2 connector will fix this issue. The owner has ordered a new PCM bracket (both pcs) and a C2 connector pigtail. He is going to bring his car to my house for the repairs. Our plan is to first replace the C2 pigtail. Then carefully ring out all wires for both TAC connectors. If this does not cure the problem, then we will then conduct SWAPTRONICS and take the TAC module from my car (identical 2002 C5Z06) and try it on his. The Service Column Lock may have an impact on this problem. The owner indicates he has an LMC5, and I will verify install as part of the troubleshooting.

 

Sounds like you've done some good work so far and have a solid plan to figure it out. Let us know what you find. Hopefully the new connector will clear up the issues.

 

Thanks. In the back of my mind is 99% of the time, electrical/electronic problems have only one true root cause. So I didn't say anything about the traction control DTC, thinking it is a result of the car going into limp mode. The FSM is not useful at all for troubleshooting the APP, TB and TAC system. However, the Tech 2 and other scan tools have a pretty good TAC section in that the "health reports" are useful in ruling out modules. Since the APP and TPS both showed correlation, my conclusion is wiring/connector, or bad module. TAC modules are a little hard to come by, and expensive, so lacking sound trouble shooting in the FSM, swaptronics may help, once wiring and connector troubleshooting is concluded.

Quick question. If the wires ring out OK, does anyone have insight into how the pins come out of TAC connector C2? I didn't notice a place to push in a release tool. I would prefer not to solder in a pigtail if I could just swap busted housing for the good one. The actual contacts look OK, just all the plastic busted from the 100mph glancing impact that took out the RF fender.

 

Post a pic of that connector.

 

This is what good TAC C2 connector looks like. When I pulled the connector from the car, the gray translucent contact guide was missing, and the internal latches that hold that guide in place were broken. When I get the new one in hand I hope I canfind out how to release the contacts from the housing, then slide the original ones back in. I didn't want to tear the connector up too much because he will have to drive the car into his trailer to bring it to my place.

 

It was the C2 connector after all. It turns out the gray translucent guide perrforms 2 functions. First is to guide the wire contacts into the pins of the TAC module. The second function is to secure the pins in position. The white tabs you see in the photo below have a lock detent that locks in a groove of each pin.


The white part also has two locks that hold the gray part in place. What was happening, is that while the contacts WERE making electrical contact with pins, the white latches were not binding the contacts in place, the pins just moved them further into the case of the connector. Also the rocket scientists that reassembled the car, left a broken PCM mounting bracket,so the TAC module flopped around. The owner expected that once the RF fender was painted and placed by the repair shop, they properly tended to internal damage. THIS CLEARLY WAS NOT THE CASE, AND SOMEONE IS IN FOR A SCOLDING FROM A ONCE LOYAL CUSTOMER. Once any of the pins lost contact, the system would see a fault and put the car in limp mode. With16 pins loose any one of them could have sent an upsetting message. Fortunately we have a local Corvette Salvage business in nearby Charlotte (VettePros 704 320 0073) that had a used connector so properly building up the connector corrected the problem. The TAC module was OK, and once we buttoned up and cleared codes, the car runs great.

When I first started troubleshooting I thought we would find a broken wire. This connector experience will have me looking more critically at connectors and proper assembly. The tech 2 has a good set of data views that really help in trouble shooting. You can see the correlation of the 3 APP sensors, the 2 TB sensors, and comm to the PCM. Then it will also show whether the TB is responding to Accelerator pedal requests. With everything properly connected, with KOEO the TB blade will move with pedal request. Makes for a good test of system functionality.

 

Well done