2003 Ford Ranger 4.0L 4x4 P0135 O2 Sensor Heater Circuit Pinpoint Test Guide

Model: Ford Fault Code: P0135 Posted: 2020-10-23 12:42

I own a 2003 Ford Ranger 4.0L 4x4 extended cab and am currently troubleshooting a persistent P0135 fault code (O2 sensor bank one upstream heater circuit malfunction). I've already replaced the oxygen sensor twice to rule out a faulty unit, but the P0135 code remains in memory and is triggered by KOER (Keep Old Error Reset). I'm seeking accurate pinpoint test procedures for this issue. Specifically, I need details on PCM pin numbers, correct pin positions within the O2 sensor connector, wire colors for the heater circuit, and whether a bulkhead-type connector exists in the heater circuit path. Any reliable source or step-by-step guide would be greatly appreciated. Thanks in advance!