2006 GMC Yukon P0172 and P0175 Codes After Battery Replacement and E15 Fuel Use

I do not see these codes in my vehicle's diagnostic system. This may indicate a model-specific issue or a difference in software version between vehicles.

P015B and P015D both refer to oxygen sensor delayed response in lean-to-rich conditions, specifically for Bank 1 Sensor 1 and Bank 2 Sensor 1. These codes suggest the ECM is not responding properly to air-fuel ratio changes.

The fuel alcohol percentage must be manually reset when using non-E85 fuels like E15, especially in older GM vehicles. If you don’t use E85, failing to reset the alcohol % setting can cause misfires and incorrect fuel trim calculations.

I do not have E85 in my tank. I will need to purchase a new OBD-II scanner to properly reset the alcohol percentage setting in the vehicle's system.

Currently experiencing P0101, P015B, and P015D as active codes. Additionally, P0172 and P0175 are pending. This pattern suggests a root cause issue rather than isolated sensor failure.

A reflash of the ECM is recommended to correct the virtual flex fuel sensor algorithm. While clearing codes may temporarily hide issues, without addressing the underlying software logic, the system will eventually revert to faulty calculations—leading to recurring problems.

No recall has been issued for 2012 models; however, earlier model years (pre-2011) had known issues related to oxygen sensor response and fuel trim calibration. This may explain the recurring codes in older GM trucks.

I noticed this thread switched vehicles mid-discussion—this caused confusion initially, but it's a common issue when users transition between models. While this vehicle is a 2012 model, the PIP4792D service bulletin covers up to 2011; future updates may introduce PIP4792E to cover more years. If negative trim values remain steady during closed-loop operation, it suggests the virtual flex sensor algorithm is stuck and requires a reflash for accurate calculations. This issue should be addressed by a qualified technician using proper diagnostic equipment.

My I/M Ready Test now shows a red 'X' under EVAP, while all other tests are green. This inconsistency is puzzling. I am planning to order a new OBD-II scanner—such as the Snap-on model—to ensure accurate diagnostics and fuel trim readings.

A used Snap-on OBD-II scanner is available on eBay, but be cautious of counterfeit or aftermarket 'Tech2' devices from China—they often lack accuracy and reliability.

GM began using MDI (Multi-Device Interface) software after 2010 for vehicle diagnostics. This may affect how fuel trim and sensor data are interpreted in later model years.

The transition to MDI likely started around 2008. After that, users need a subscription with AC Delco Online to access full diagnostics. While some knock-off devices exist, they do not match the performance of OEM tools like Snap-on.

I filled my tank with 25 gallons of E15. The alcohol percentage was initially 75.3% before filling; it fluctuated between 69% and 80% during the drive, settling at 78.4%. Before the appearance of P0172 and P0175, I had zero DTCs. Key readings: - Short Term Fuel Trim (Bank 1): -7.0%, Long Term: -25.0% - Short Term Fuel Trim (Bank 2): -7.0%, Long Term: -24.2% - Alcohol Fuel Percentage: 78.4% - Oxygen Sensor Output Voltage (B1S1): 0.065V, B2S1: 0.070V - Bank 2 Sensor 2 Trim: 99.2% (indicating rich condition) - Catalyst Temperature: 1034°F for both banks - Engine Coolant Temp: 195°F - Intake Air Temp: 116°F - Commanded Equivalence Ratio: 0.999 These values suggest a persistent lean-to-rich fuel trim imbalance, likely triggered by incorrect alcohol percentage input or faulty sensor response.

I had the dealer reset the alcohol percentage and fuel trims. While this resolves the immediate warning light, it does not address the root cause of the underlying fuel control issue.