Owner's Problem Description
The owner of a 2009 GMC Canyon reports that the check engine light illuminated a few days ago. After changing the gas cap, the light turned off but reappeared after two days. The truck runs fine, but now a buzzing noise is heard coming from underneath the vehicle, specifically near the passenger side rear tire. The owner seeks advice on the possible causes of the issues.
Professional Technical Analysis
The vehicle in question is a 2009 GMC Canyon, equipped with a 3.7L inline 5-cylinder engine and an automatic transmission, with an estimated mileage of approximately 80,000 miles. The owner initially addressed a check engine light by replacing the gas cap, which is a common initial step for evaporative emissions system issues. The light remained off for two days, indicating a temporary solution, but has since illuminated again, suggesting a persistent fault in the emission system. The buzzing noise emanating from underneath the truck raises concerns about potential issues with the fuel pump, automatic load-leveling pump, or emissions system components. Notably, GM fuel pumps, particularly in this model, can exhibit increased noise levels over time due to wear or design characteristics. The connection between the check engine light and the buzzing noise should be investigated, as a malfunctioning emissions system or fuel pump may trigger fault codes. It is essential to perform an OBD-II scan to retrieve any stored diagnostic trouble codes (DTCs) to pinpoint the underlying issues. Upon inspection, common fault codes might relate to the evaporative emissions system or fuel pressure issues, which could explain both symptoms. The current condition of the vehicle appears stable, but it is crucial to address the check engine light and noise for safety and efficiency. The buzzing noise, if associated with the fuel pump, may not be immediately concerning unless accompanied by performance issues or a check engine light.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Noise: The buzzing noise may be attributed to the fuel pump operation, which is often noticeable in GM trucks, especially as they age. A properly functioning fuel pump should operate quietly, but wear can cause increased noise. If the buzzing is accompanied by performance issues or abnormal pressure readings below the specified range of 55-62 PSI, the fuel pump may need replacement. - No performance issues noted, buzzing noise from under the truck near the fuel tank.
- Evaporative Emissions System Leak Detection: The buzzing noise could also indicate the operation of the leak detection pump, a component responsible for checking the integrity of the evaporative emissions system. This pump may activate intermittently, particularly if there are fault codes related to the EVAP system. If the check engine light is illuminated, it is likely that the system has detected a leak or malfunction. - Check engine light illuminated, potential fault codes related to the EVAP system.
- Automatic Load-Leveling Pump: If the truck is equipped with an automatic load-leveling system, the buzzing noise may originate from the leveling pump. This pump engages when the vehicle senses a change in load, adjusting the suspension accordingly. If the pump is malfunctioning, it may run continuously or intermittently, causing noise. - Noise located near the rear passenger side, where leveling pump might be located.
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 Scan: Begin with an OBD-II scan using a professional diagnostic scanner or GeekOBD APP to retrieve any diagnostic trouble codes (DTCs). This will provide insight into the check engine light and help identify any faults in the EVAP system or related components. Pay attention to freeze frame data for conditions when the code was set.
- STEP 2 - Visual Inspection: Conduct a thorough visual inspection of the fuel system components, especially the fuel pump and EVAP system. Look for any signs of leaks, damaged hoses, or disconnected lines. Ensure the gas cap is properly secured. Additionally, inspect the area near the rear passenger side for any signs of wear or damage related to the leveling pump.
- STEP 3 - Fuel Pressure Testing: Use a fuel pressure gauge to measure the fuel pump output pressure at the fuel rail. Ensure that the pressure falls within the specified range of 55-62 PSI. If the pressure is below this range, it may indicate a failing fuel pump. Also, listen for any unusual noises from the pump during operation.
- STEP 4 - Functional Testing of EVAP System: If DTCs indicate a potential issue with the EVAP system, perform a functional test of the leak detection pump. This may involve applying a vacuum and checking for leaks in the system. Ensure that the pump activates properly and there are no leaks present.
