Q: What Do Transmission Error Codes Tell You?

Using transmission error codes is a necessary procedure for a transmission technician since automatic transmissions have been computer controlled for over 20 years. The transmissions currently in use are very different to diagnose and repair than transmissions from decades ago. For correct operation, transmissions rely on accurate electrical inputs from multiple sensors. A transmission control module (TCM) processes the inputs, “decides” what the correct action is for the current conditions, and sends out commands to actuators. The required training, electrical understanding, tooling, and diagnostic skills required of transmission technicians have all increased dramatically. Fortunately, the automatic transmission control systems are designed to be able to provide some clues to a technician about what “might” be faulty. These are the fault codes or error codes. A technician obtains them from the vehicle’s control module using a scan tool. Codes may indicate issues with the speed sensors, shift solenoids, pump pressures, valve body circuits, or slipping clutches. The fault can be the TCM itself, programming calibration, or electrical wiring, connections, or grounds for any of these. The scan tool and code doesn’t tell a technician what part to replace, but does provide direction to an experienced, trained technician in the diagnostic process.