Owner's Problem Description
The owner reports a persistent P0452 EVAP code on their 2000 Chevy Blazer. They have replaced the fuel pump, fixed a previous vacuum leak, and replaced the purge valve. The charcoal canister was checked and is not blocked. A pressure sensor and gas cap were also replaced. Recently, the vehicle has been stalling when the temperature exceeds 85°F, only restarting after cooling down. The owner suspects a wiring issue at the pressure sensor, as it shows no voltage while the PCM provides 5 volts at the connector.
Professional Technical Analysis
The 2000 Chevy Blazer with approximately 150,000 miles exhibits a persistent P0452 EVAP code, indicating a fuel tank pressure issue. The owner's extensive repair history includes replacing the fuel pump, fixing vacuum leaks, and ensuring the integrity of the charcoal canister and purge valve. However, the vehicle has recently developed a new issue where it stalls after approximately 25 minutes of driving when ambient temperatures exceed 85°F. This suggests a potential thermal-related failure, possibly in the ignition system or fuel delivery components. The absence of voltage at the pressure sensor indicates a possible wiring fault, which may also contribute to the stalling issue. Given the vehicle's history, a comprehensive diagnosis of the EVAP system, including leak detection and pressure regulation functionality, is essential. The stalling issue could be linked to the ignition control module or coil pack, both of which have been replaced, suggesting that further investigation into the fuel pump operation and electrical connections is warranted, especially in relation to thermal effects on components.
Possible Causes
Most common causes (ordered by frequency):
- Wiring Issue at Pressure Sensor: The lack of voltage at the pressure sensor indicates a potential wiring fault or bad connection. The expected voltage is typically around 5V when the key is in the run position, which suggests that the wiring harness may be damaged or corroded. The pressure sensor should be tested for continuity and resistance, expected values should be around 0.5-5V under normal operating conditions. - No voltage reading at the pressure sensor, verified 5V at PCM connector, potential wiring issues.
- Thermal Failure of Fuel Pump: The stalling issue after prolonged driving in warmer weather could indicate that the fuel pump is overheating. Fuel pumps can fail under thermal stress, especially after extended operation, leading to insufficient fuel delivery when hot. Continuity tests and fuel pressure checks (should maintain 35-45 PSI) should be performed to confirm pump operation. - Stalling after 25 minutes of driving, fuel pump operational noise, vehicle starts only after cooling down.
- Ignition Control Module (ICM) Failure: The stalling issue may also be related to the ignition control module, which could fail under thermal conditions. If the ICM experiences overheating, it may cause intermittent spark delivery, leading to stalling. The module should be tested for proper operation and resistance values typically between 0.5-2.0 ohms for the ignition coil. - Intermittent stalling, recent ICM replacement, potential overheating issues.
- EVAP System Leak: Although previously repaired, EVAP systems are prone to leaks due to aging components. If there is a leak in the system, it can trigger the P0452 code and lead to fuel pressure imbalances. A smoke test should be performed to verify the integrity of the EVAP system after all repairs. - Previous repairs on EVAP system, P0452 code present, smoke test recommended.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Code Retrieval: Begin with a thorough scan using the GeekOBD APP or a professional OBD-II scanner to retrieve current and pending fault codes. Pay special attention to freeze frame data associated with the P0452 code, which may provide insight into the conditions under which the fault occurs. Document all findings for further analysis.
- STEP 2 - Electrical Testing: Test the wiring and connectors associated with the pressure sensor. Use a multimeter to check for continuity and resistances. Expected resistance values should be minimal (< 5 ohms) for good connections. If resistance is high or continuity is absent, repair or replace the wiring harness as needed.
- STEP 3 - Fuel Pressure Check: Perform a fuel pressure test using a gauge connected to the fuel rail. Ensure the pressure remains between 35-45 PSI while cranking. If pressure is low, further investigate the fuel pump operation and any potential blockages in the fuel lines.
- STEP 4 - Smoke Test for EVAP System: Conduct a smoke test to check for leaks in the EVAP system, focusing on areas such as the charcoal canister, purge valve, and associated lines. This test can help identify any hidden leaks that may trigger the P0452 code.
