1998 BMW 740iL Stuck in Reverse Only: Fault Codes P0733 and P0720 Explained
Hi everyone, My 1998 BMW 740iL has suddenly stopped moving forward in Drive and is now only able to move backward in Reverse. This behavior started gradually, with the car becoming increasingly erratic before completely locking into reverse. A mechanic friend diagnosed the issue using an OBD2 scanner and found two fault codes: P0733 (Gear 3 Ratio Incorrect) and P0720 (Output Speed Sensor Circuit Malfunction). The vehicle is equipped with a 4.4L V8 engine, but I'm unsure of the transmission type. I'd like to know what these codes mean in practical terms and how they might be causing this issue. Any insights or troubleshooting steps would be greatly appreciated. Thanks in advance! Note: This problem is specific to the 1998 BMW 740iL model with automatic transmission, and the fault codes are consistent across multiple similar vehicles reported online.
P0733 indicates an incorrect gear ratio in Gear 3, which may result from a faulty transmission sensor or internal mechanical issue. P0720 points to a malfunctioning output speed sensor circuit — this is often due to damaged wiring, loose connections, or a failing sensor itself. Recommended steps: Inspect the wiring harness and connector for the output speed sensor located near the transmission. Test the sensor with a multimeter if possible, and ensure it's properly grounded. If either component fails, replacement may be necessary. This issue is commonly reported in 1998 BMW 74 or 740iL models with automatic transmissions.