2000 Mazda Millenia S P1540 OBD II Code: Causes, Fixes, and DIY Solutions
I own a 2000 Mazda Millenia S with a 2.5L Miller cycle engine, approximately 41,000 miles, and an automatic transmission. Recently, the vehicle began experiencing difficulty accelerating at around 2,000 RPM. This issue is accompanied by the check engine light and a previously illuminated traction control off warning — though the traction control light has since turned off, the check engine light remains on. Using an OBD II scanner, I retrieved fault code P1540: 'Manufacturer Control Vehicle Speed Idle Speed Control Auxiliary Input'. This code relates to the vehicle's idle speed and auxiliary input system. I'm wondering if this is a serious issue or simply a minor malfunction. Is it possible to diagnose and fix this problem myself? Any insights or recommendations would be greatly appreciated.
I experienced the exact same symptoms. I took my car to AutoZone, where they also found code P1540. The technician couldn't immediately identify the root cause. I cleaned my air filter and intake hose as a first step. However, after one week, the issue returned. I haven’t had any further repairs done yet. Has anyone else resolved this on their Mazda Millenia S? If so, what steps did you take? My vehicle is a 1999 model.