DanMurphy

Code P0135

replaced O2 sensor twice, to no luck incase first was defective. Replaced harness plug, to no luck. Check power voltage 13v. Ohmed out wires to 6” from pcm… all to no luck at 0.1 ohms on all 3.

what could be causing the p0135 sensor 1 heater malfunction besides the o2 sensor and wiring?

MoneypitLS4

Could be a fuse or exhaust leak prior to sensor

DanMurphy

I found and fixed issue.

Ohmed out all 3 wires to pcm. 0 ohms, so the other possibility is wire sheathing poor. So yes, found





the wires going through main wire harness are catching magnetic fields.

pulled the wires out of harness, completely entangled, so had to cut and splice back in. Wrapped in electrical tape once over. Good enough to stop the magnetic fields from other wires in harness. Separated alternator power wire and O2 sensor wires into new loom.

going back to loom in the main harness once that arrives.

MoneypitLS4

Glad you found your issue. Seems like on these cars the wires fail more than the sensors/switches do. They're all just about a 1/2" too short, too stiff, too many together, not enough gauge for the current, just all around poor quality wiring. Guess that's why they call it a GM parts bin car. I also had to break out all the wiring like you did, except mainly to make room around the truck intake swap (Which does fit BTW). I ditched the original battery terminals and did individual direct run 2/0 from battery to starter, to fuse box, and one to alternator. Then 2/0 ground to motor and one to chassis. The positive battery terminal finally stopped corroding, but the parasitic draw is still there. (That's the radio/BCM)