Q: My check engine light is on even after replacing both O2 sensors.

When a car has as many miles as your has, the problems really start to stack up until it seems like everything happens at once. Reading and interpreting the codes can be more subtle than it appears.The guys at the auto parts stores who do it for free often do not have the training to fully understand what the codes mean. When the check engine light comes on, it can have multiple codes, and if you are not careful reading, you may not see everything that is there. A code that says you have no reading on a sensor could mean that there is damage to the wiring or the connector rather than the sensor itself. An EGR code that says you have low flow doesn’t necessarily mean you need an EGR valve. It could mean the EGR passages in the manifold are clogged. Your best bet is to have the codes read and interpreted by someone with the training and the experience to give you the whole picture. You can do that at your convenience by contacting YourMechanic. They can send a technician to your home or office to check out your Buick and let you know what it will take to solve your problem.