Last night’s videos provided some crucial insights into engine diagnostics, particularly regarding the P0171 code, which indicates a system too lean in bank 1. I also captured additional data to further analyze this issue. A key takeaway was learning about the “Freeze frame” mode on code scanners. This function is invaluable as it captures engine parameters at the precise moment a trouble code is triggered. This is a detail I previously overlooked, highlighting the continuous learning in automotive diagnostics.
Another important piece of information was understanding how Short Term Fuel Trim (ST FTRM) and Long Term Fuel Trim (LT FTRM) values work together. These percentages combine to show the total fuel deviation. By examining the freeze frame data for my P0171 code, I took two screenshots to analyze the conditions when the code was set.
Code Scanner Freeze Frame Data Displaying Fuel Trim Values and Vehicle Speed
The first image clearly shows that the P0171 code was activated when the vehicle was traveling at 54 mph. This observation aligns with my driving experience, as the code seems to appear primarily during highway speeds, above 50 mph. It doesn’t typically occur during city driving or stop-and-go traffic. Looking at the fuel trim values, the short term fuel trim is 10.2, and the long term fuel trim is 24.2. These values combined equal 34.4. From my understanding, exceeding a combined fuel trim value of 30 is sufficient to trigger the P0171 code, confirming a lean condition.
The second screenshot provides further engine data captured in the freeze frame.
Code Scanner Freeze Frame Data Displaying RPM, Load, Coolant Temperature, MAF, and MAP Readings
This data reveals that when the code was set, the engine RPM was 1559, the calculated load was 64.7%, and the coolant temperature was 187 degrees Fahrenheit. Again, these figures support the idea that the P0171 code is triggered under higher speed driving conditions, with the engine at operating temperature and under a moderate load. Interestingly, the code light often extinguishes when driving at lower speeds around town, suggesting the lean condition is more pronounced at higher speeds.
However, I noticed something peculiar in this second screenshot: both the Mass Air Flow (MAF) and Manifold Absolute Pressure (MAP) sensor readings are 0.0. This seems unusual and potentially erroneous. While I have replaced both sensors recently and believe they are functioning correctly under normal driving circumstances, these freeze frame readings are concerning. It’s possible that the freeze frame function did not capture data for these sensors at that specific moment, as zero readings from both would likely cause more severe engine performance issues and potentially other error codes. This is something I need to re-examine to ensure the accuracy of the sensor readings.
Finally, I conducted a test on the power brake booster. After shutting off the engine and waiting for five minutes, I was able to get approximately 2.5 assisted presses on the brake pedal before it became firm. While I am uncertain if 2.5 presses is within the normal range, it suggests the brake booster is likely holding pressure. However, the brake booster’s functionality may not be directly related to the P0171 “System Too Lean Bank 1” code, and this test might be a separate diagnostic path.
In conclusion, while these observations provide valuable data points, the root cause of the P0171 code remains unclear. Further investigation is needed, particularly regarding the MAF and MAP sensor readings in the freeze frame data, and potential vacuum leaks or fuel delivery issues that could be contributing to the lean condition at higher speeds. Continued troubleshooting is necessary to resolve the “system too lean bank 1” issue and prepare for the upcoming emissions test.
