When your 2021 Subaru Forester's cruise control stops working and the check engine light is illuminated, these issues are likely connected. Subaru's cruise control system is designed to disable itself when the engine management system detects certain faults that could affect vehicle operation.
Why Engine Faults Disable Cruise
The cruise control system relies on stable engine operation to maintain set speeds. When the ECM detects a fault that could cause erratic engine behavior—such as misfires, sensor failures, or emission issues—it disables cruise control as a safety precaution. This prevents the system from attempting to maintain speed with an engine that may not respond predictably.
Common Engine Codes Affecting Cruise
Codes that typically disable cruise include: misfire codes (P0300-P0304), oxygen sensor faults (P0131-P0134, P0151-P0154), mass airflow sensor issues (P0100-P0104), throttle-related codes, catalytic converter efficiency codes (P0420, P0430), and EVAP system faults. Not all check engine codes disable cruise—it depends on the severity and type.
Symptoms Combination
You'll notice the check engine light illuminated along with cruise control refusing to engage. The cruise main light may come on when activated, but pressing SET does nothing. On EyeSight-equipped models, adaptive cruise and lane keeping may also be affected. Engine may or may not have noticeable performance issues.
Diagnostic Approach
Use a Subaru Select Monitor or OBD-II scanner to retrieve the check engine code(s). Research whether the specific code is known to disable cruise control. Address the engine fault according to diagnostic procedures for that code. After repair, clear codes and verify both check engine light and cruise control return to normal operation.
Resolution
Fixing the underlying engine problem restores cruise control function. This could range from simple repairs like replacing an oxygen sensor to more involved work like addressing a misfire condition. Once the ECM sees normal operation and codes are cleared, cruise control re-enables automatically.