| Original thread here: Code 21 Woes I've been admittedly lazy working on this, so that's why so much time has passed. Thought I'd add this for future troubleshooters to add to my previous list. After unsuccessfully being able to procure a secondary ECU as Cjw3 suggested, I did myself some edumacating. I never thought harness continuity was an issue since it was brand new. I did test it from the PTU connector to the coil pack connector when I was running out of ideas. I never did check from the ECU to the other PTU connector, because I *incorrectly* assumed since I was getting 12V at the coil pack connector I had continuity back to the ECU. I did not realize that voltage was a reflection of the ignition relay! As a newb, I disconnected the PTU, and tested the connector to verify this. After realizing that there were two separate signals, I did some digging in the FSM to find out what the actual ECU output voltage of the ignition signal is to the coil packs (read as PTU)....0.1 volts. From there it was a simple test that I never thought to do, and take readings at the PTU connector. Sure enough on my dead cylinder, I got 0V! As a final confirmation, I tested continuity on all 6 wires back to the ECU connector AND took those same voltage readings directly off the ECU. Same results. To summarize, unfortunately it's a faulty ECU. And while it would have been much simpler to have had a secondary ECU to plug in and verify this, it's good to get a little better understanding of the ignition system.
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