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SOLVED. Ignition coil connector was the issue. I cut the connector off the harness, disassembled it and found moisture had been trapped inside the connector, causing corrosion (especially on the 12v pin). Due to the corrosion voltage was leaking from the 12v pin to the signal wire pin. I checked the other connectors and found moisture in all of them when I removed the seal! The kicker is I think it is coolant, from some unknown event in this car's history. So I replaced all the connectors. Since I replaced all 6, I decided to source connectors from various places to compare. I bought a kit that included 4 connectors, terminal pins, retaining clips, plug and wire seals for $18 on Amazon. I bought a plug from Volkswagen for $32, and I bought a coil connector pigtail repair kit from Deutsche Autoparts for $34. Surprisingly the quality of the cheap Amazon connectors was good, and you can't beat $18 for 4! The drawback is it takes a long time to connect all the wires and terminals. A long time. The coil connector pigtail repair kit from Deutsche Autoparts is great. Comes wired, ready to splice in to the harness and includes the tool to remove the terminal pins. Time saver for sure, and basically the same price as the OEM un-wired housing. Amazon kit: https://www.amazon.com/gp/product/B07GXPDS6Y/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1 Deutsche Autoparts kit: https://www.shopdap.com/vw-audi-ignition-coil-connector-pigtail-4b0973724.html
Thank you for the recommendation. I didn't know if those sites are legit.
Did some probing with a multi-meter, many hours of googling, and spoke with an ecu repair company called Module Experts, and figured my ecu was probably bad and causing the #6 coil to melt. Sent the ecu off to Module Experts, got it back, put it in, drove about 50 miles and melted another #6 ignition coil. So I figured wrong, or Module Experts are a scam...or some combination of both. Thinking of replacing the wiring harness? Really tough to diagnose without a wiring diagram.
Where can I find a wiring diagram for the ignition system? (coils, power, ecu, etc)?? Thanks in advance!
Update of doom... This morning I swapped in another coil. Intention was to start the engine and start jiggling wires. Car ran perfect. Drove it about 20 miles (30 minutes). Ran fine. No problems. Ok.... Let it sit for a few hours then tried again. When I started the engine, it shuddered on idle as if under load, but revved ok. Drove it less than 1 mile and the coil erupted like a volcano! Howver the electrical wiring plug is fine. No burning or melting. What the heck would cause such immediate disaster so randomly?
Yes, I read through the entire saga! The only direction I can think now is a bad spot in the wiring to consistently fault the circuit? Going to go back through the wiring carefully.
Hey all, new member, first post. I've spent hours scouring this site and others for info, but to no avail. I would appreciate any insight! 2004 Cayenne 3.2L Bought the vehicle a few days ago with a misfire. Towed the vehicle home and began to diagnose. - Cleared the code history (there was a laundry list of codes stored from previous owner replacing fuel pumps and other things). - Test drove. Bad misfire. P0276 – Injector 6 – circuit low P0273 – Injector 5 – circuit low P0270 – Injector 4 – circuit low P0356 – Ignition coil F, primary/secondary – circuit malfunction - I checked the fuses for the coils and indeed the 20amp in #8 was blown. Replaced. Cleared the codes. Test drove. Ran well for a few minutes then misfire and blown fuse again. The number 6 coil was melted, signs of burning from within. P0276, P0273, P0270, P0300, P0306, P0305, P0304 P0356 – ignition coil F circuit failure (coil 6) - Next I replaced all 6 ignition coils with Beru coils, and replaced all spark plugs with NGK IZKR7B. Wires look ok, all the harness plugs at the coils seem fine. No burning. I also cleaned the inside of the coil/plug cavity with a soft brush and blasts of compressed air to clear any debris (cleaned it with the old plugs in of course). Also cleaned grime from the coil seats. Cleared the codes. Took it for a test drive. Test drive lasted about 23 miles (30 minutes) before it started running poorly. - Number 6 coil MELTED AGAIN! Brand new coil melted. Fuse did not blow this time, and the only code is P0356. I cleared the code, swapped in an old coil for 6, started and immediate misfire, immediate P0356. Is this an ECU problem? How can I diagnose? Help?? I attached a few photos of the two burned coils, and the old plug from 6.