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Continued saga of poor running....new codes

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I have been posting my problems for a while. Starting with random and persistent misfires on one bank (5-8). I have replaced all coil packs and plugs and the problem is less frequent. After a couple of days poor running I ran my Durametric to get the following codes....

Vehicle electrical system voltage via main relay - No signal/communication, test conditions are not-completed, fault is currently active and is not causing a DTC light

- Upper limit value exceeded, test conditions are not-completed, fault is currently active and causing a DTC light

O2 Sensor Circuit Bank 2 Sensor 1 - Implausible signal, test conditions are not-completed, fault is not currently active and is not causing a DTC light

Can anybody help me identify an underlying cause(s)


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On the 03 CTT one winter I had the P2146 and I believe it was either an injector or a wiring harness to a bank of injectors. I know at the time my favorite tech said it was rare and he hadn't heard of it. I also had the P0150 with this as it was a result of the P2146. Once P2146 cleared it did as well.

I had P1549 multiple times. For me it was a result of dirty connections from various front parking assist sensors. Dirt got inside the wiring harnesses.

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  • 4 weeks later...

Implausible signal usually means a dead or dying O2 sensor. Since the car runs in closed loop when it's warmed up and at part throttle, it'll try to maintain stoich using the O2 sensor as a feedback mechanism. If the O2 sensor was fine - then you'd likely see a rich or lean code if the injectors weren't doing their job.

The relay voltage and voltage at the injectors could be related, but not sure how. I'd start with swapping your bank 1 and bank 2 injectors to see if the problem follows. That would help rule out a bad injector(s) from a bad harness.

Misfires on Cyl 5-8 is a symptom of a problem. Could be an injector harness, or could be the failing O2 sensor.

If it were me, I'd start with getting the battery system checked to rule that out. It's like a poltergeist lives in the car when the battery is low. After that, i'd get a fresh set of primary O2 sensors in there. Realistically, they last 100K miles, especially on an FI car. They could go another 50K miles without throwing a code, but you'll be running really rich and well below what's considered "ideal conditions." Pull the harness off the ECU or disconnect the battery to reset the long term fuel trim data once the O2 sensors are in, and then drive the car for at least 50 miles if you restart the car and it's not misfiring. Rescan and see what comes back. If you're still misfiring on Bank 2, swap the injectors with the other side and see if the misfires follow. If they don't, then you know you have a harness problem on Bank 2. If you have a bad injector, you could probably get one at a salvage yard, pull the rest of your injectors, and send them for cleaning and flow testing (15 bucks an injector).

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