KOEO & KOER Codes
WARNING: This page is about a different car, the 2004 Mercury Monterey and 2004 Ford Freestar. However, it is still accessible from the selected car via links, so may be relevant.
These DTCs indicate faults are present at time of testing. A hard fault may cause Malfunction Indicator Light (MIL) to illuminate and remain illuminated until fault is repaired. The MIL is located on instrument cluster and may be labeled SERVICE ENGINE SOON or CHECK ENGINE. If KOEO or KOER DTCs are retrieved during KOEO ON-DEMAND SELF-TEST or KOER ON-DEMAND SELF-TEST, see DIAGNOSTIC TROUBLE CODE DEFINITIONS under QUICK TESTS to find appropriate system test to perform.