Q: Check Engine light comes on and goes off

If the speedometer is not working but the rest of the instrument cluster is, the issue is probably the vehicle speed sensor. This sensor is the main input to the control module for speedometer control. The problem could also be with the wiring or the speedometer itself. There are hundreds of reasons the Check Engine Light might be on. The powertrain control module (PCM) takes inputs from dozens of sensors. It then uses this information to control outputs such as fuel delivery and emissions equipment. If the PCM detects a problem anywhere in the system it will illuminate the Check Engine Light. A failed vehicle speed sensor could cause both of the problems you are having. A trained professional, such as one from YourMechanic, will be able to inspect your vehicle’s speedometer issue and Check Engine Light to give you a definitive answer for what repairs are needed.