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P0133 and P0420 Fault Diagnosis: O2 Sensor Replacement for 1996 Ford Explorer 2WD 6-Cylinder

Model: 1996 Ford Explorer 2WD 6cyl Fault Code: P0133 Posted: 2008-03-11 09:55

Hello everyone, I've been experiencing P0133 and P0420 diagnostic trouble codes on my 1996 Ford Explorer 2WD 6-cylinder truck. The Check Engine Light has been flashing intermittently over the past several months. My question is: If I replace both the upstream (before catalytic converter) and downstream (after cat) oxygen sensors, what are the chances that this will clear the P0420 code? I've read online that sometimes replacing the rear O2 sensor can resolve a P0420 issue because faulty readings from the rear O2 sensor may trigger the code. I'm looking for expert insight on whether sensor replacement is a viable solution or if there are more likely underlying causes—such as catalytic converter failure, exhaust leaks, or other system issues. Thanks in advance, Jocasio

Related fault codes
P0133P0420
Comments (3)
Anonymous 2008-03-11 13:17

Replacing the oxygen sensors won't cause harm, but without a proper diagnosis, you can't be certain it will resolve the issue. The root cause could involve other components such as the catalytic converter or exhaust system leaks. Do you have access to an OBD-II scan tool that allows real-time monitoring of oxygen sensor readings? I recommend first visually inspecting all sensor connections and reviewing these resources for more detailed guidance: - http://www.obd-codes.com/p0133 - http://www.obd-codes.com/p0420

Anonymous 2008-03-11 13:36

Thanks for the reply! I already had my truck scanned, and both P0133 and P0420 codes were recorded. So I'm wondering if replacing the O2 sensors—especially the rear one—might clear the P0420 code. Is there a way to perform an actual diagnostic check on the oxygen sensors? If so, how can I do it without specialized equipment? Appreciate your help!

Anonymous 2008-03-11 16:06

Accurate diagnosis of oxygen sensor performance requires a scope (oscilloscope) to capture real-time voltage waveforms. Without this, any replacement is essentially a guess. I'd recommend purchasing a diagnostic scope from the dealership or an auto parts store, replacing both sensors, clearing the DTCs, and then monitoring whether the P0420 code returns. However, the likelihood that sensor replacement alone will resolve both codes—especially P0420—is very low. The issue is likely deeper in the exhaust system or catalytic converter.