A "check engine" light is both an alarming and uninformative warning indicator on your car's dashboard; to understand the cause of this warning light, the vehicle can be taken to an auto repair shop or auto parts store to retrieve a more precise warning code. These codes provide a list of possible causes for the check engine light's appearance. A Volkswagon Passat's code P1875 indicates a problem caused by either the engine control module or transmission control module.
Check the engine control module (or ECU) at an auto repair shop. The ECU controls the fuel-to-air mixture, ignition timing and other operations required for an engine to function.
Check the transmission control module (TCU) with a transmission repair specialist. The TCU collects data from sensors both in the vehicle and in the ECU to calculate the proper timing for changing gears to provide optimum speed, fuel economy and shift quality.
Choose a repair shop that is trustworthy and provides a reasonable price for repairs. Have them repair the ECU or TCU, whichever is causing the problem in the vehicle. After repairs are completed, monitor the performance of your car by paying attention to how the car feels while driving and being alert for any dashboard warnings; return to your mechanic if the problem persists.