Code 1123: Oxygen Regulation Stop

Fault code is set if oxygen regulation is unable to operate within control range. Fuel mixture may be too lean because of additional air entering intake system. A too rich condition may be caused by a sticking (open) fuel injector.

Check idle speed and mixture (CO level). Refer to the ADJUSTMENTS article. If fuel mixture is too lean, check intake system for leaks. If fuel mixture is too rich, check fuel pressure. Refer to the BASIC TESTING article. If fuel pressure is okay, replace leaking fuel injector(s).