Why does the engine warning light come on after an oil change?
2 Answers
Reasons for the engine warning light illuminating after an oil change: 1. Poor fuel mixture combustion: Poor combustion of the fuel mixture can lead to engine carbon buildup or knocking issues, which are detected by the engine's oxygen sensor and reported to the ECU, triggering the warning light. 2. Sensor issues: When sensors such as the coolant temperature, crankshaft position, air flow, intake air temperature, or oxygen sensors are damaged, have poor connections, or experience signal interruptions, the car's ECU cannot obtain engine data, causing the engine warning light to illuminate. 3. Carbon buildup issues: Over time, carbon deposits accumulate inside the engine. These deposits can alter the engine's design parameters and, due to their unstable nature and heat retention, can cause uncontrolled ignition, leading to engine knocking and the illumination of the engine warning light.
I just finished repairing my car and encountered many cases where the engine light came on after an oil change. Most of the time, it was due to either overfilling or underfilling the oil, causing the oil pressure sensor to report an error. The computer might misinterpret this as a fault because the standard oil level should be safely in the middle of the marked lines. Another common reason is accidentally disturbing the sensor wiring harness during the oil change, loosening the connection and causing false signals. It could also be due to using the wrong type of oil, such as a viscosity mismatch, which the engine can't adapt to. For older cars, improper installation of the oil filter can easily trigger the light. I recommend checking yourself first: pull out the dipstick to see if the oil level is appropriate—if it's too high or too low, drain or add oil accordingly. Then start the vehicle and wait a few minutes to see if the light goes off. If it stays on, don’t force-drive the car to avoid engine damage; instead, quickly use an OBD scanner to check the fault code or go directly to a professional workshop. During regular maintenance, remember the oil specifications and avoid buying cheap, low-quality oil to prevent many issues.
