Symptoms

Start from what the car is doing. Each page says how serious it is and which codes and parts it points to.

Check engine light came on after getting gas Severity: Monitor
Check engine light with loss of power Severity: Inspect soon
Rough idle with the check engine light on Severity: Inspect soon
Car shaking with the check engine light on Severity: Inspect soon

Is the check engine light flashing? Stop driving and read this first.