PO154 and PO307 Fault Codes on 2003 Chevy Express 2500 6.0L: Diagnosis and Solutions
My 2003 Chevrolet Express 2500 6.0L diesel is consistently throwing diagnostic trouble codes PO154 and PO307. I recently replaced both upstream oxygen sensors (one on each side), as the truck only has two upstream O2 sensors. The symptoms are intermittent—about half the time, the vehicle runs normally. Other times, it exhibits a rough idle and poor acceleration, as if one cylinder is misfiring. It typically performs well under light load or at idle but begins to miss when load is applied or during acceleration. The truck has accumulated 445,000 miles, which raises concerns about potential wiring issues—specifically, whether a wire may have worn through and caused a ground fault. Any insights into diagnosing this issue would be greatly appreciated. Is it possible the O2 sensor replacement was ineffective due to using substandard parts? Or could there be an underlying engine or ignition problem? Jerry
Using a diagnostic scanner, check the O2 sensor readings—look for whether they are 'stuck' in a specific range. If stuck, it may indicate a faulty sensor or wiring issue. Why did you replace the O2 sensors? Ensure you used OEM- or quality-grade sensors; aftermarket or low-quality parts can cause persistent codes and misdiagnoses. Technically, PO154 (O2 sensor circuit malfunction) and PO307 (cylinder 7 misfire) are not simply out of bias range—investigate the root cause. For PO307, perform a spark check, verify injector pulse, inspect for leaking injectors, and conduct a compression test to rule out mechanical issues.