Jeep Cherokee Forum - P0171 Possible Remedy

Hello all.

So I have suffered the P0171 fault on my 03 WJ. When the issue first started happening, I noticed through research that this is a very common issue with the vehicle and there really does not seem to be very much guidance, antidotes are plentiful. My experience with this may be different but perhaps it is the most common issue in regards to the lean condition.

My scan tool is an ELM bluetooth device using Torque Pro ($5) -- BUY IT!!!

Here were my symptoms, starting from when I start the car up cold:

engine runs great
no economy issues
engine heats up
engine begins to run poorly, sometimes while driving, or after starting after a pit stop to get coffee or you preferred beverage along the way to work
while running the scan tool reading for codes, pending code for P0171
FUEL TRIMS WERE MAXED OUT, OVER 32 FOR LTFT AND STFT
engine would run poorly, fuel economy would tank, often would set a cylinder misfire code in bank 1

In terms of troubleshooting:

I ended up buying an O2 sensor, upstream for the bank.....unnecessary.
I also contemplated poor injector performance and poor fuel pumper performance

Rather, I took note that the issue was occurring after a period of time post the engine warming up.

On the Torque scan tool app, while observing "real time information", i selected to view O2 voltages and fuel status. This was the important part, OPEN AND CLOSED LOOP. When in Open loop, the ECU is running the engine fuel trims based upon a preset mixture setting determined by the factory. When the vehicle warms up, it enters Closed Loop mode and begins to use the O2 sensors for fuel management. That being said, the O2 sensors effectively don't work while in open loop, or you could say the ECU in not monitoring them for Built-in-Testing. That then will allow you to make the determination that the fuel injectors, the coil, and the pump and in good working order because they work perfectly fine under Open loop operation. The O2 voltages were all normal, except for sensor 1, it was 0Vdc. If the system was truly lean, you would expect a low voltage, however, not 0Vdc. Now, that either means the O2 sensor is bad, or there is a wiring issue.

I pulled over, took the phone app with me, being that it is bluetooth, I moved the wiring harness to the sensor while the engine was running and observed the voltage on the sensor improving. There was obviously a wiring issue.

To confirm the diagnosis, with the Torque scan tool app, there is a graphing selection to allow you to analyze engine data. Using the graph tool, select Bank 1 LTFT/STFT, O2 sensor bank 1 sensor 1 and O2 bank 1 sensor 2. I moved the harness to a position that provided good continuity to the sensor and watch the data. With the improved voltage from the sensor, the fuel trims immediately improved to perfect!

I then check the ground and signal wire for shorts and opens. I found that the signal wire had shorted to ground, causing the 0Vdc condition.

Long write-up and I am not the best at explaining, however, i have read through many other forums for this issue and almost all have the same issue, to include the fuel trims.

So, if you have this issue, I would suspect there to be a wiring issue in the engine wiring harness to the o2 sensor.