The BMW E46 is known for its sporty handling and refined driving experience. However, like any vehicle, it can experience issues, especially with age. One common problem with the E46 Auto Transmission is entering “limp mode,” significantly limiting performance. This article addresses potential causes of limp mode, specifically focusing on error codes P0715 and P0720, often related to the transmission input and output speed sensors. We’ll explore whether cleaning or replacing ABS sensors can resolve these issues.
The symptoms described by an E46 owner experiencing limp mode include an illuminated gear indicator light, accompanied by the ABS and brake warning lights, particularly in hot weather or after encountering bumps. The vehicle struggles to engage reverse initially but may do so after driving forward a short distance, albeit with a harsh shift. Diagnostic codes P0715 (Input/Turbine Speed Sensor Circuit Malfunction) and P0720 (Output Speed Sensor Circuit Malfunction) point towards potential problems with the transmission speed sensors.
While these codes suggest faulty transmission sensors, the intermittent ABS light activation in hot conditions or after hitting bumps raises the question of a possible connection between the ABS system and the transmission limp mode. Could a dirty or malfunctioning ABS sensor be triggering false positives in the transmission system? The owner replaced the MAF sensor and checked the battery, ruling out these common culprits. Resetting the battery connection temporarily cleared the limp mode, but it returned upon acceleration, indicating a persistent underlying issue.
Before replacing the transmission speed sensors, it’s worth investigating the ABS system. ABS sensors monitor wheel speed and relay this information to the ABS control module. This data is also used by the transmission control module for various functions, including shift timing and torque converter lockup. A faulty ABS sensor can disrupt these processes, potentially leading to limp mode. Cleaning the ABS sensors is a relatively simple procedure and might resolve the issue if contamination is interfering with their operation.
However, it’s crucial to understand that while a dirty ABS sensor can contribute to broader system malfunctions, it’s less likely to be the direct cause of the specific P0715 and P0720 codes. These codes directly implicate the transmission input and output speed sensors. Replacing these sensors is often the necessary solution. While the owner plans to replace the thermostat and transmission fluid thermostat, these are unlikely related to the limp mode issue, as it occurs during acceleration rather than overheating.
In conclusion, while cleaning the ABS sensors is a worthwhile maintenance step and might resolve intermittent ABS issues, it’s unlikely to fix the core problem causing the P0715 and P0720 codes and the resulting limp mode. Addressing these codes likely requires replacing the transmission input and output speed sensors. Further diagnosis with a specialized BMW scanner might provide more specific insights before replacing components.
