P0452 (Large EVAP Leak): This code means the system has detected a significant leak in the EVAP system. This system is designed to capture fuel vapors from the tank and prevent them from escaping into the atmosphere. Leaks can be caused by several things:
* Loose or damaged gas cap: This is the most common cause. Try tightening the gas cap first. If it's cracked or damaged, replace it.
* Leaks in the EVAP system hoses: Inspect all hoses and connections related to the EVAP system for cracks, splits, or loose fittings. These hoses run from the gas tank, through various components (like the canister purge valve), and often to the intake manifold. Look for vacuum leaks as well.
* Faulty purge valve: The purge valve controls the flow of fuel vapors into the engine to be burned. A stuck-open or stuck-closed valve can cause this code. This requires testing or replacement.
* Cracked or damaged fuel tank: Less common, but possible. This is difficult to diagnose without specialized equipment.
* Faulty EVAP canister: The canister absorbs fuel vapors. A damaged or clogged canister will not function properly.
P0463 (Fuel Level Sensor Circuit High Input): This code means the PCM (Powertrain Control Module) is receiving an inaccurate or inconsistent signal from the fuel level sensor. This sensor tells the gauge how much fuel is in the tank.
* Faulty fuel level sensor: The most likely culprit. This sensor is often located in the fuel tank and can be damaged or fail over time. Replacement may be needed. Sometimes cleaning the connection can resolve the issue temporarily, but a replacement is generally recommended.
* Wiring issues: Check the wiring harness and connectors leading to the fuel level sensor for damage, corrosion, or poor connections. A break or short in the wiring can cause this code.
* Faulty fuel pump module (if integrated with sensor): While you've replaced the fuel pump, if the fuel level sensor is integrated into the pump module, the new module might have a faulty sensor component.
Troubleshooting Steps:
1. Start with the simple stuff: Tighten the gas cap. This is the easiest and most frequent solution for P0452.
2. Visual inspection: Carefully examine all hoses and connections related to both the EVAP system (P0452) and the fuel tank (P0463). Look for cracks, loose connections, or any signs of damage.
3. Gas cap test: After tightening the gas cap, clear the codes and drive the vehicle. If the code returns, the gas cap is likely faulty.
4. Smoke test (EVAP system): A smoke test is the best way to find small leaks in the EVAP system. A professional mechanic typically performs this test.
5. Fuel level sensor test: This requires a multimeter and some knowledge of automotive electrical systems. You'll need to test the resistance and voltage at the sensor to see if it's functioning correctly.
6. Professional diagnosis: If you're not comfortable performing these tests yourself, take your Blazer to a trusted mechanic. They have the tools and expertise to diagnose and repair the problem efficiently.
Important Note: Replacing parts without proper diagnosis can be expensive and ineffective. Focus on systematically checking the most likely causes based on the code descriptions, starting with the simplest solutions. If the codes persist after the initial checks, seeking professional help is recommended.
