97 Chevy Blazer 4.3L 4WD with P0117, P0131, P0151, P0171, P0174, and P0300 - Diagnosis & O2 Sensor Issues
I recently purchased a 1997 Chevrolet Blazer 4-door automatic with the 4.3L Vortec engine and 4WD. The vehicle starts easily but runs roughly at idle and exhibits sputtering, hesitation, and bogging when accelerating—though it never dies. After scanning for trouble codes, I'm seeing multiple DTCs: P0300, P0117, P0131, P0151, P0171, and P0174 (with P0171 and P0176 appearing twice). I've already replaced the distributor cap and rotor. I also recently installed a new fuel pump and filter, but the symptoms persist. Spark is confirmed in the wires and coil pack. From research, I understand: - P0300 indicates random misfires, which can be caused by lean conditions or faulty sensors. - P0171 and P0174 indicate a lean condition on Bank 1 and Bank 2, respectively—commonly due to vacuum leaks or malfunctioning oxygen (O2) sensors. A lean mix could lead to random misfires. - P0131 and P0151 point to low voltage in the O2 sensor circuits for Bank 1 Sensor 1 and Bank 2 Sensor 1, suggesting potential issues with those sensors or their wiring. My question: Given that I have both P0171/P0174 (each appearing twice) along with P0131 and P0151, should I prioritize replacing the O2 sensors? Or are there other root causes I should investigate first? Additionally, what does P0117 mean exactly? DTC P0117 is 'Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage'—does this indicate a faulty ECT sensor or wiring issue? How critical is this code in relation to engine performance and fuel trim? Any guidance on troubleshooting steps, such as checking fuel pressure under KOEO conditions or inspecting the ECT sensor wiring, would be greatly appreciated.
A diagnostic code does not confirm a part is faulty—it only indicates a problem within that system. DTC P0117: Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage — this means the ECT sensor is not providing accurate temperature readings due to low voltage, which can affect fuel mixture and engine performance. DTC P0131: HO2S Circuit Low Voltage Bank 1 Sensor 1 DTC P0151: HO2S Circuit Low Voltage Bank 2 Sensor 1 — these suggest the oxygen sensors are not functioning properly or have faulty wiring, which can cause incorrect air-fuel ratio readings. Recommended troubleshooting steps: - Use a fuel pressure gauge to check fuel pressure under KOEO (Key On, Engine Off) conditions. Observe if pressure drops significantly within 5 minutes—this indicates potential fuel system leaks or pump issues. - Inspect wiring and connectors for the ECT sensor and O2 sensors for corrosion, damage, or loose connections. - Consider replacing the O2 sensors as a next step, especially given repeated P0131/P0151 codes. Prioritize checking the ECT sensor first—since it directly affects engine temperature readings and fuel trim. A faulty ECT can cause lean conditions (like P0171/P0174) and contribute to misfires (P0300).