that may be my mistake, it asked me for the year and i wasnt sure so i put 2000.

 

I asked the question again but specified its drive by wire and this is what I got.

Yes — 100% this can still be the case even though the car is drive-by-wire. Drive-by-wire has nothing to do with how the PCM calculates fuel when the engine is cold. The ECT sensor is one of the primary inputs the PCM uses to decide fuel enrichment, start-up strategy, and idle behavior. If the ECT sensor sends a false “ice-cold” temperature only when the ambient temp is below ~67°F, the PCM will still dump excessive fuel, the engine will run extremely rich, then stall — regardless of drive-by-wire or cable throttle. What looks like a throttle-by-wire problem (like the throttle blade closing) is actually the PCM reacting to the rich condition and falling RPM, not the cause of the no-start. DBW cars still rely heavily on the ECT sensor for fueling, spark, and idle control, so a bad reading will shut them down just like a cable-throttle car. So yes — a failing or temperature-sensitive ECT sensor/wiring can absolutely cause this exact start-and-die behavior even on a DBW C5.

 

did you data log it while the issue was happening?

 

this was its response when i typed in what you said here.
That history 100% confirms the ECT circuit is the root of the problem — just in a more specific way. Here’s what your new info tells us very clearly: --- ✅ When the ECT wires were cut, the PCM saw “–40°F” Whenever the ECT circuit is open (broken wire, bad splice, high resistance): The PCM defaults to –40°F It maxes out fuel enrichment It turns both radiator fans on The engine runs pig–rich or won’t run at all That’s exactly what you saw before the wires were repaired. --- ❗ Now that the wires were spliced back together, one of two problems is still present: 1. The splice is introducing extra resistance when cold A poor crimp, poor solder, moisture in the splice, or stiffened wire insulation can cause the connection to become intermittent only when temperatures drop. When the resistance increases just enough at ~67°F or lower, the PCM sees a false low temp reading again, dumps fuel, starts-and-dies, and fans may run depending on severity. This explains why the problem only exists when cold and why heating the area near the bumper (where the harness runs) brings it back to life. --- 2. The ECT signal wire is partially damaged inside the loom The alternator dropping on it could have: Stretched the copper inside the insulation Broken strands internally Caused a weak spot that only "opens" when cold contraction occurs This is extremely common after a wire is accidentally cut and rejoined. --- 3. The ECT sensor may have been damaged by running the car with the circuit open It's not as common, but it happens: A voltage spike or short during cranking may have weakened the sensor. Now the sensor behaves normally warm but reads wrong when cold. Given how cheap the sensor is, replacing it is usually part of the fix. --- 📌 WHY THIS EXACTLY MATCHES THE 67°F SYMPTOM Copper wiring and solder expand/contract with temperature. At ~67°F and below, a weak splice or internal wire break will: Increase resistance Drop the signal voltage Make the PCM falsely think the engine is MUCH colder than it actually is ⇒ PCM dumps fuel⇒ Car starts briefly, runs rich, dies⇒ Throttle snaps shut as RPM collapses⇒ Heat the area → wire expands → runs perfect This is textbook ECT circuit damage. --- ✔️ What to do to fix it 1. Check the ECT harness repair Look for: Twisted wires with no solder Crimps that can pull apart Electrical tape instead of heat-shrink Green corrosion inside wire Splice too close to the sensor connector (common failure point) Best repair is: Strip both ends clean Solder the wires Use adhesive heat-shrink Wrap the harness cleanly 2. Replace the ECT sensor anyway They often get damaged from: Shorts Over-fueling Running with open circuit Thermal shock during the initial failure They're cheap and prone to temperature-related failures. 3. CLEAR fuel trims after the repair Disconnect battery or use scanner → Clear trims and codes. --- 🎯 Bottom Line Given the history, the problem is 100% in the ECT circuit or the ECT sensor — the alternator drop and cut wires created a temperature-sensitive wiring fault that now only shows up below ~67°F. This is absolutely the cause of the rich start-and-die condition and matches every one of your symptoms. --- If you want, I can tell you exactly where that wire runs, how to test it with a multimeter, or how to permanently bulletproof the repair.

 

Here is the complete, single-response guide to diagnosing and permanently fixing your C5 Corvette’s 67°F no-start issue, including PCM pin locations for testing the ECT circuit. This covers everything end-to-end. --- ⭐ FULL FIX GUIDE — C5 Corvette 67°F No-Start / Rich Start-Then-Die / Fans On — After ECT Wires Were Cut Because the ECT wires were accidentally cut during alternator installation, and the car was started with the wires open, the PCM defaulted to “–40°F,” which caused both fans to run and the engine to run extremely rich. Even though the wires were later repaired, the symptoms below 67°F prove that the splice or internal copper strands are damaged, causing high resistance or intermittent opens only when cold. This is a textbook temperature-sensitive ECT circuit failure. This can absolutely cause start-then-die, overly rich mixture, unstable idle, and throttle shutdown — even on drive-by-wire cars. --- 🔎 1. WHERE THE ECT WIRES RUN The ECT sensor is on the driver side cylinder head, just behind the upper radiator hose.It has two wires: Yellow = ECT Signal to PCM Black = PCM Low-Reference Ground These wires run: 1. From the sensor 2. Under/near the alternator bracket (exactly where yours was damaged) 3. Up the front of the engine 4. Into the main engine harness 5. To the PCM on the passenger side behind the fender liner This alternator drop incident almost always damages the conductor further up the loom, not just in the visible cut. --- 🧪 2. DEFINITIVE MULTIMETER TESTS (Cold and Warm) You’ll test the wires from the ECT connector directly to the PCM pins. PCM Connector Key Your C5 PCM has two plugs: C1 (Red) C2 (Blue) ← this is the one with the ECT circuits ECT Wire Pinouts (C5 Corvette LS1/LS6): ECT Signal (Yellow) → PCM C2 (Blue) Pin 26 ECT Ground (Black) → PCM C2 (Blue) Pin 59 --- 🧪 TEST A — SIGNAL WIRE CONTINUITY 1. Unplug the ECT sensor. 2. Remove PCM Blue Connector (C2). 3. Probe: Yellow wire at the ECT connector Pin 26 at the PCM (C2) 4. Measure resistance. What you should see: ✔ 0.2–0.8 ohms when warm or room temp✔ Stable reading Failure signs: ❌ Resistance climbs when cold (1–20 ohms)❌ Reading flickers or jumps when harness is wiggled❌ Open circuit (OL) until you warm the area with your hand or heat gun If any of these happen → the signal wire is damaged internally from the alternator incident. --- 🧪 TEST B — GROUND WIRE CONTINUITY Probe: Black wire at ECT connector Pin 59 at PCM (C2) Same rules: ✔ Less than 1 ohm❌ Resistance increases or opens when cold❌ Reading changes when you wiggle the loom If the ground wire is compromised, the PCM will also default to –40°F and add extra fuel. --- 🔎 3. FAST “WIGGLE TEST” (Very Revealing) With key ON (engine not running): 1. Watch ECT °F live data on a scanner. 2. Wiggle the section of harness under the alternator and toward the front of the engine. 3. If temp drops, spikes, or jumps → bad splice or internal break. Even if you don’t see big jumps, it can still be failing only below ~67°F due to contraction of copper. --- 🧰 4. WHAT THE PROBLEM ACTUALLY IS One of these is happening inside your repaired wiring: Poor crimp Poor solder Moisture inside the splice Copper strands stretched or broken internally Wire jacket cracked, letting in corrosion Splice too close to hot/cold metal Butt connector expanding/contracting with temperature When cold, resistance increases → PCM thinks engine is extremely cold → dumps fuel → engine starts rich then dies. Heat expands the copper → signal returns → car starts normally. --- 🔧 5. PERMANENT FIX — THE RIGHT WAY Cut out the ENTIRE repaired section, plus 1–2 inches of wire on each side until you reach shiny copper. Then: 1. Make NEW splices: Strip ends Solder only (no crimps) Slide adhesive heat-shrink over each joint Heat until glue flows and seals the splice 2. Re-loom the harness: Wrap with automotive-grade Tesa tape Ensure the harness cannot rub under the alternator Add slack, but not enough to reach the pulley 3. Replace the ECT sensor Running the engine with the wires open can damage it electrically.They often become temperature-sensitive afterwards. --- 🔄 6. RESET THE PCM After finishing repairs: Disconnect battery 10 minutesor Clear trims and codes with a scanner This removes the bad fuel trims learned from the rich condition. --- 🏁 7. EXPECTED RESULT After repairing the damaged wiring and replacing the ECT sensor: ✔ Starts normally at any temperature✔ No rich stumble✔ No start–then–die✔ No fan-on-at-startup behavior✔ Throttle will behave normally✔ Fuel trims return to normal This EXACT symptom (perfect above 68°, fails below 67°) is caused by temperature-dependent resistance in the ECT circuit — which fits perfectly with the alternator-drop wire damage. --- If you want, I can guide you with: Exact wire colors at the PCM Photos of the PCM connector layout The best replacement ECT sensor How to test the sensor itself with a meter Just tell me your C5’s year.

 

This would be the absolute first place I would start.

There is likely either still a wiring issue here (solder cracks perhaps), or the sensor itself may have also been damaged during the event.

I remember posting back in early October in this thread, stating that the issue was likely not related to the tune but rather a wiring, sensor, or hard parts issue. I still believe that, even more so after reading this update that was not previously disclosed. If the issue started after the incident with the temp sensor, I wouldn't waste time on anything else until this possibility was completely eliminated.

 

I agree 100%, this has got to be the problem. I thought this was the problem before even finding out that had happened.

 

The tuner did. He said he saw nothing that was a red flag. I ran the coolant temp sensor by him, and he said he would've seen anything wacky on his HPTuners while tuning it. I thank you very much for trying to help me. I am going to install a new AC/Delco ECT sensor tomorrow or Wednesday. The only problem I have now is that being in Florida, I may not get a cold enough morning for several days now. I'll post the results as soon as I get them. HAPPY THANKSGIVING EVERYONE!!!!👍🦃🦃.

 

This problem has been present for 3 or 4 YEARS....Long before I broke the pigtail wire.....

 

I wouldn't expect that the tuner would see any red flags with the sensor readings once the car is running. The nature of this issue is that the sensor seems to report fine once it's running. So unless the tuner is there with the scanner hooked up while the crank-start-die issue happens, I wouldn't expect him to see anything at all.

Do you have a scanner available to you? Would be interesting to see what data this sensor is reporting when in key-on-engine-off state at ambient temps below the 67° threshold.

Also, just replacing the sensor might not be the solution. There could also be an issue with your wiring repair. Sometimes even a good solder job will develop a crack in this sort of repair scenario. I would recheck that wiring repair and/or reheat the solder just to make sure the connection is perfect.

 

I didn't realize this was the case. So then the solder job might not be suspect, but the sensor itself could still be a problem.

As I mentioned above, do you have a scanner to check ECT data with the key on, engine off, when ambient temp is below 67°F?

 

I dont see how that would work out though, while he was tuning the car the sensor was working properly. you would have to have to be data logging when You were below 67 degrees and the issue was happening. Next time you have below 67 degrees hook up the lap top and data log in that exact moment and see what happens. If it were me id go ahead and replace the sensor with a an oem quality sensor and verify all wiring. Thats a fairly cheap and easy solution. I know in a sense its throwing parts at it but unless your outside in the cold with a laptop and a multimeter I dont really see any other way and no problem man, ive been through hell and back with my truck and while im sure there are guys here much more qualified then me ive still turned many wrenches in my life and dont mind offering the help.

 

sounds like he should refer back to the can of freeze spray previously mentioned and have the lap top and multimeter ready.

 

The fans have not come on again since I repaired the wire. The wire looked fine, nice virgin looking copper strands. But again, this problem first developed at least 4 years ago. It's just that I'm finally getting tired of it. Wouldn't shorted or high resistance wiring also throw some sort of code? I'm certainly not arguing with you guys, because even though I'm good on mechanical stuff, I'm not so good on wiring diagrams and using DVOM. I am pretty competent on checking for continuity on the DVOM meter, and on soldering, as my father, who was very good on electronics, first showed me how to properly solder when I was only 8 years old. I am in a HOA, so my resources are limited until I get back home to Michigan and my lift. Not supposed to even work on your car here. But if you guys can help instruct me, I'll try to do as much as I can while I'm down here. Thanks, again....

 

I don't have a data logger or HPTuners. I'm totally at the mercy of my tuner, or someone who has a data logger.....

 

The tuner says he has data logs both under and over 67°. He is having a few issues with his own car (suspension and exhaust), and he wants to get his stuff working, so he took a couple of weeks off to do all he needed. Still, he emailed me yesterday, and told me he will try to send them out ASAP. He's banging his head against the wall on all this, too. He's going back into the tune history 7 or 8 years ago, looking for anything he can find that may be wrong with the tune! As soon as he sends the files, I promise to post them. I'm starting to think you guys are right about the ECT sensor, and/or circuit. It could even be a bad fit at the male/female pins at the PCM. I have a new OEM ECT sensor coming. Be here tomorrow. The old one is 10 years old, and for just $20, it's worth it to me to at least eliminate the sensor itself from the equation. If you'll help walk me thru how and where to test, I'll be happy to try. I have a DVOM. and know how to do voltage and continuity tests. The next few days will be tough as Thanksgiving is almost here. I'm really looking forward to finding out just what the Hell is causing this issue ........

 

Read my message from 12:34 today. That gives details how to test the wiring. Also I would strongly suggest getting a laptop and downloading hp tuners. My truck is on holley and I downloaded an app called any desk on it and my tuner can literally link his laptop to mine and take full control on my laptop while its hooked to my truck. I don't have to send him anything, he can see it live as it happens.

 

Hey, Tommy. I looked but cant find a post here that was made yesterday at 12:34????

 

this one, my apologies 12"31

 

No worries. Just thought it didn't post. Anyway, got my new ECT sensor yesterday. Probably won't install it until tomorrow. HAPPY THANKSGIVING guys.....🦃🦃🦃