1996 Silverado 5.7L Vortec Engine Fault Codes P0141, P0172, P0175, P0300, P0719 - Diagnosis and Solutions
I own a 1996 Chevrolet Silverado Z71 with a 5.7L Vortec engine. The vehicle is currently displaying the following diagnostic trouble codes: P0141, P0172, P0175, P0300, and P0719. The truck exhibits several symptoms including hesitation at startup, occasional coughing or internal backfiring, rough idle, and a noticeable loss of power during acceleration. While the engine runs smoothly at higher RPMs, it becomes progressively worse as it cools down. A distinct 'nose burning' smell is present, indicating potential fuel-related issues. I recently cleaned the Mass Air Flow (MAF) sensor, but this did not resolve the problem. Interestingly, when I disconnect the battery cables and reset the SEL (Service Engine Light), the truck runs normally for approximately 30 to 60 minutes without any warning lights. After that period, symptoms return gradually, and the SEL reactivates. I’ve been advised by several mechanics that certain fixes may not address the root cause. I’m wondering whether these codes point to faulty oxygen sensors or an intake system issue. How can I verify if my O2 sensors are functioning correctly and accurately reporting a rich air-fuel mixture? Any guidance on diagnosing these issues would be greatly appreciated, especially in terms of fuel pressure, sensor performance, and potential component failures.
I recommend grouping the codes into two main categories: • Likely Related Issues: - P0172: System Too Rich (Bank 1) - P0175: System Too Rich (Bank 2) - P0300: Random/Multiple Cylinder Misfire Detected Start with a fuel pressure test under KOEO (Key On, Engine Off) conditions. Observe if the fuel pressure drops by X psi within five minutes — this could indicate a failing fuel pump or internal leak. Do NOT use an oiled air filter; it can interfere with sensor readings and cause false rich conditions. Ensure the engine reaches proper operating temperature (around 195°F) before testing. A 'spider' assembly issue (part of the fuel rail system) is a strong possibility — this could explain both the misfire and rich mixture codes. • Separate Issue: - P0141: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2) - Check fuses and verify 12V supply on the pink wire at Bank 1 Sensor 2. • Another Independent Code: - P0719: Torque Converter/Brake Switch B Circuit Low - Inspect the brake light switch — it controls multiple functions including cruise control and torque converter clutch release. A faulty switch may cause this code to appear. Regarding your question about O2 sensor performance: Use an OBD2 scanner to monitor O2 sensor voltage readings in real time. Then, intentionally introduce a vacuum leak (e.g., by temporarily sealing the intake) and observe if the sensors shift from rich to lean — this will confirm whether they are responding correctly. Additionally, check for fuel trim values on the scan tool to assess engine control logic. *Note: KOEO means Key On, Engine Off — essential for accurate fuel pressure testing without engine load.