2004 Jeep Grand Cherokee P051, P0152 & P0155 O2 Sensor Faults After Replacement and Wiring Fix
I'm looking for advice on persistent O2 sensor fault codes P051, P0152, and P0155 on my 2004 Jeep Grand Cherokee. I initially suspected a faulty oxygen (O2) sensor, so I replaced Bank 2 Sensor 1. Using the vehicle's onboard computer, I observed that the signal level was previously maxing out at 1000mV—indicating a wiring issue. After diagnosing and repairing a shorted wire, the reading now ranges from as low as 60mV to up to 850mV, which appears normal when monitored with an oscilloscope. However, after both repairs and resetting the engine light, the same fault codes persist. I've also tested the other three O2 sensors, all of which show similar signal readings and appear functional. The issue seems not to be a sensor failure but possibly related to the heater circuit or wiring integrity. Any insights or recommendations on how to resolve these persistent codes? Specifically, could it be an aftermarket or non-OEM sensor causing intermittent heater circuit issues? Vehicle: 2004 Jeep Grand Cherokee (4.7L engine likely, though this should be confirmed).
I suspect you're running the 4.7L engine—yes? All three codes reference Bank 2 Sensor 1 (B2S1), which aligns with that configuration. Let me know if it's a 4.0L model, as there are rare California-emission variants with four O2 sensors. My best guess: You may not have installed an OEM-quality O2 sensor—perhaps an aftermarket or DIY replacement? This could lead to incomplete heater circuit operation. The symptoms suggest the heater circuit is shorted to signal, possibly intermittently. Code P051: O2 Sensor Heater Circuit Low Code P0152: O2 Sensor Shorted to Voltage (Bank 2 Sensor -1) Code P0155: O2 Sensor Heater Failure (Bank 2 Sensor -1) Note: The heater circuit is critical for proper sensor operation; a faulty or incomplete heater circuit can cause erratic readings and persistent fault codes even after replacing the sensor. If you're using a non-OEM part, it might be worth verifying compatibility and quality. Also, ensure all wiring connections are secure and properly insulated.