* Wheel Speed Sensor Issues: This is probably the most common reason. The traction control system relies heavily on wheel speed sensors to detect wheel slip. A faulty sensor (or multiple faulty sensors) will cause the Slip light to illuminate. Furthermore, incorrect wheel speed data will also disrupt the engine's calculations (particularly in vehicles with automatic transmissions and sophisticated engine management), triggering the CEL.
* Transmission Problems: Problems within the automatic transmission (if equipped) can affect both systems. A failing transmission can cause erratic wheel speeds (activating the slip light) and send incorrect signals to the engine control unit (ECU), causing the Check Engine light to illuminate. This might include issues with the transmission's speed sensor or internal problems affecting gear selection.
* Vehicle Speed Sensor (VSS) Problems: The VSS provides speed information to both the engine control system and the traction control system. A malfunctioning VSS can lead to inaccurate speed readings, triggering both lights.
* ABS Issues: The Anti-lock Braking System (ABS) is closely tied to traction control and often shares sensors. A problem within the ABS system, such as a faulty ABS sensor or module, could trigger both lights.
* ECU Problems: Although less likely, a malfunctioning ECU could misinterpret data from various sensors, leading to both lights illuminating. This is a more serious issue requiring professional diagnosis.
* Wiring Harness Issues: A damaged or corroded wire in the harness connecting sensors to the ECU could lead to inconsistent or faulty signals.
What to do:
You'll need to get the codes read from the car's onboard diagnostic system (OBDII). An auto parts store often offers this service for free. The diagnostic trouble codes (DTCs) will pinpoint the specific problem. This information is crucial for accurate diagnosis and repair. Simply resetting the lights won't solve the underlying issue; it will only temporarily mask the problem. Ignoring it could lead to more extensive and costly damage.
