2009 Chevrolet 3500 6.0L Diesel - P0121 and P0440 Fault Codes: Diagnosis and Fixes
I'm experiencing both P0121 and P0442 fault codes on my 2009 Chevrolet 3500 with the 6.0L engine. I've already replaced the accelerator pedal and throttle position (TP) sensor, and performed a brake cleaner spray test to check for leaks—no signs of vapor or fluid leakage were found. Any suggestions on how to resolve these codes? Specifically, could cleaning the Mass Air Flow (MAF) sensor help with P0121? Also, is this issue more common in stock vehicles without aftermarket modifications? P0121: The predicted airflow and MAP sensor readings are outside the calibrated range for more than 3 seconds. P0442: This relates to evaporative emissions system leakage—could it be intermittent or related to a known Technical Service Bulletin (TSB)?
First thought: P0121 should be addressed before dealing with the evaporation-related P0442 code. Did you clean the Mass Air Flow (MAF) sensor? A dirty MAF can cause incorrect airflow readings and trigger P0121. Is your vehicle stock, or have any aftermarket parts been installed? P0121 explanation: The predicted air flow and MAP sensor data exceed the calibrated range for more than 3 seconds. Note: If P0442 is intermittent, it might be covered by a Technical Service Bulletin (TSB). Since P0121 appears first, this could indicate a root cause related to airflow sensing.