2002 Isuzu Rodeo Sport P0135 O2 Sensor Heater Circuit Malfunction: Diagnosis and Fix Guide

Is this a 2002 Isuzu Rodeo Sport with a 3.2L V6 engine? Did you confirm the correct bank (Bank 1) and location of the sensor? Avoid using generic 'one-size-fits-all' sensors—these can cause issues. The 20-amp fuse for the O2 heater circuit is typically located in the under-hood fuse relay box. It's unlikely to be a single fuse serving all four sensors, but it's worth checking. Also verify that there’s no short in the wiring harness at Bank 1 Sensor 1 (B1S1), especially around the return wire and heater circuit.

Yes, it's a 6-cylinder V6. I replaced the sensor on the driver’s side exhaust pipe—right after the engine. I used a Bosch OEM 'Exact-Fit' replacement from Pep Boys. I'll check the fuse box later today. I'm not sure what 'check the wiring harness at B1S1 sensor return shorted htr voltage' means. Could you clarify? Do I need to inspect the wire connected to the new sensor, or where it plugs into the exhaust system? I’m willing to do the work myself, but I don’t know how to locate parts on this vehicle. Any help is much appreciated—this issue is very frustrating.

B1S1 stands for Bank 1 Sensor 1 — that's the correct designation for the oxygen sensor in the first bank of the engine.

I understand B1S1, but I don’t know what 'check the wiring harness at B1S1 sensor return shorted htr voltage' means. Do you mean inspecting the wire connected to the new sensor or where it’s plugged into the exhaust? I had trouble reaching up into that area—how exactly should I go about checking this? Please clarify and suggest specific steps. I'm ready to learn and do this myself.

Use a DVOM (Digital Volt-Ohm Meter) and consult the vehicle’s wiring diagram to verify continuity, grounding, and voltage in the circuits. One circuit should show about 5V (for the sensor), while the heater circuit should have approximately 12V. If these are missing or incorrect, it may indicate a wiring issue or an incompatible sensor. Many aftermarket sensors don’t match the required heater resistance as specified by the PCM—this can trigger a P0135 code even after replacement.

I’m sorry to sound ignorant, but what exactly is a DVOM and how do I use it? What setting should I use on my multimeter, and what voltage or resistance values should I expect when checking the wiring harness? Thanks for your patience! Also—how can an oxygen sensor be incompatible? What does that mean in practice?

Jeff means using a DVOM (Digital Volt-Ohm Meter) and a wiring schematic to check continuity, grounding, and voltage. For the O2 sensor circuits: one should read about 5V (sensor signal), and the heater circuit should show around 12V. Many aftermarket sensors—especially 'Exact-Fit' ones—may not have the correct heater resistance required by the engine control module (PCM). This can cause a P0135 code even after replacement. I agree with Jeff: return to Pep Boys and get an OEM sensor from the dealer instead of a third-party brand.

I spoke with a local dealership about the O2 sensor. After being shocked by the $185 price, they confirmed that Bosch sensors are reliable. They also noted that Bank 1 Sensor 1 is located on the right side of the vehicle when viewed from the driver’s seat. I mistakenly replaced the left-side sensor (which was actually Bank 2). After swapping it with the right-side one and clearing codes, I received a new code: P0140—EGR Valve Stuck Open. What is an EGR valve? How do I fix it? Will this code go away once the P0135 is resolved—or does it indicate a separate problem?

Quick update: After swapping the sensors, all diagnostic codes have cleared. Confirmed that Bank 1 Sensor 1 is on the right side of the vehicle when viewed from the driver’s seat. Thanks to everyone who helped—your input saved me over $200 in parts and labor!

So the EGR issue has also been resolved? Did you have the O2 sensor positions mixed up? A helpful tip for others: when diagnosing O2 sensors, unplug the suspected one, clear codes, then start the engine. If a fault appears but changes to 'Bank 1 Sensor 1 High' instead of 'Low', that confirms it's the correct sensor location.