P0153 Fault Code on 2007 Infiniti FX35 with VQ35DE Engine - Diagnosis and Sensor Replacement Guide
I own a 2007 Infiniti FX35 equipped with the VQ35DE engine (a Nissan-sourced unit). The vehicle was originally purchased new in the USA in 2007 and later imported to Europe, where access to official Infiniti services was limited, requiring me to perform many repairs myself. Last year, I noticed a significant increase in fuel consumption—rising from around 15 mpg to 10–11 mpg. A mechanic advised replacing the Mass Air Flow (MAF) sensor, which I did. However, this did not resolve the issue. Another suggestion was to replace both pre-catalyst oxygen sensors. I purchased two Walker-style oxygen sensors and replaced the first sensor on bank 2. After a short test drive, the Malfunction Indicator Lamp (MIL) illuminated immediately, and the engine light displayed code P0153—indicating a problem with the second pre-cat O2 sensor. Upon inspection, I realized that both sensors must be replaced simultaneously. The second sensor is notoriously difficult to access, but I successfully completed its replacement. To my surprise, after reinstallation, the fault code returned—but now it points back to the first sensor (bank 2). This has left me confused. I have thoroughly inspected the wiring harness, removed and reinstalled the sensor, checked for air intake leaks, and verified exhaust system integrity. No obvious issues were found. Given that both sensors are now installed and no physical faults are evident, what could be causing this recurring P0153 code? Is it possible that the first sensor is simply defective or incompatible with the vehicle's ECU?
The most likely causes are either an incompatible sensor, a defective unit, or a wiring/circuit issue. I recommend checking for an original equipment (OE) sensor from a Nissan or Infiniti dealer. If the original sensor is labeled with its manufacturer—such as 'Nissan' or 'Bosch'—using that brand may improve compatibility and reliability.