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1996 Mustang GT: P0136 and P0156 O2 Sensor Fault - Downstream Sensors Explained

Model: 96 Mustang GT Fault Code: P0136 Posted: 2006-05-02 15:24

Hello everyone, my 1996 Mustang GT has recently triggered the Check Engine light. The diagnostic codes retrieved are P0136 (O2 sensor circuit bank 1 sensor 2) and P0156 (O2 sensor circuit bank 2 sensor 2). I'm trying to understand which oxygen sensors these refer to — are they the ones located near the exhaust headers or at the rear of the vehicle? Additionally, I've already replaced the upstream O2 sensors in the front (near headers) last year. Now I'm wondering if it's time to replace the downstream sensors at the back. Can someone clarify what 'B1 S2' and 'B2 S2' mean in this context? Thanks for any insight! Mileage is approximately 95,000 miles.

Related fault codes
P0136P0156
Comments (5)
Anonymous 2006-05-02 16:34

It's unlikely both sensors failed simultaneously. A wiring issue should be considered first — check the connectors, harnesses, and fuses for any signs of damage or corrosion. The codes P0136 and P0-156 typically point to downstream oxygen sensors located after the catalytic converter. These are usually found at the rear of the exhaust system, not near the headers. A thorough inspection of wiring and grounding points is recommended. Good luck — please update us on your findings. What's your current mileage? - Jeff

Anonymous 2006-05-02 16:44

I don't believe it's a wiring issue since I've already inspected all the wires and found no visible damage. My car has around 95,000 miles on it. Last year, I replaced both front O2 sensors (near headers), but I'm not sure if that was enough or whether the downstream ones in the back are now failing. I'm still confused about what 'B1 S2' and 'B2 S2' mean — does 'bank 1' refer to the left side of the engine, and 'bank 2' to the right? Any clarification would be greatly appreciated. - Jeff

Anonymous 2006-05-03 11:50

P0136 and P0156 refer to downstream oxygen sensors in Bank 1 and Bank 2 (after the catalytic converter). Since you've already replaced the upstream sensors, it's likely these downstream sensors are now failing. Replacing both downstream O2 sensors is a common solution for this issue on a 1996 Mustang GT.

Anonymous 2006-05-03 13:48

Thanks so much for the help! Your input has been very valuable. I'll keep you updated once I complete the replacement and test drive the car.

Anonymous 2009-03-13 20:27

I experienced the same issue on my 1996 Mustang — P0156 indicated a downstream O2 sensor failure after the catalytic converter. The code initially showed only one faulty sensor, but replacing both downstream sensors resolved it completely.