Transmission Control Module (TCM) - This handles the transmission, including items like transmission fluid temperature, throttle position, and wheel speed.

Vehicle Control Module (VCM) - Another module name that controls the engine and vehicle performance.

Engine Control Module (ECM) - This controls the actuators of the engine, affecting things like ignition timing, air to fuel ratios, and idle speeds.

Some of the more common ECU types include: On new cars, these are all typically microcontrollers. Tuning features on the ECU can allow the user to make the engine function at various performance levels and various economy levels.

These can be standard from the manufacturer, reprogrammable, or have the capability of being daisy-chained for multiple features. They monitor and control many functions of the car. The ECU can refer to a single module or a collection of modules. It is a 16 pin connector that can tell you which protocol your car communicates with, depending on which pins are populated in it.īefore we get too much farther, let's make sure we understand all the keywords used in these protocols. You can access this system through the Data Link Connector (DLC). The HardwareĪny vehicle manufacture from 1996 or later is required by law to have the OBD-II computer system. Unfortunately, the actual protocols themselves are not available publicly (if only they'd open source!), but we've attempted to collect and clarify as much as possible. If you or your mechanic has ever read the DTCs (Diagnostic Trouble Codes) on your vehicle, they are using OBD-II. Learning how to work with those protocols also means that you can determine what that Malfunction Indicator Light (MIL) (aka the Check Engine Light) on your dash is referring to when it tells you there's an engine problem. Saving the planet is great (shout out to you citizen scientists!), but what this also means is we can access other features of the car and collect information from and on those parts.

In other words, OBD is the language of the Engine Control Unit (ECU), and it was designed to help fight emissions and engine failures.

OBD systems are designed to monitor the performance of some of an engine's major components including those responsible for controlling emissions. On-Board Diagnostics, or 'OBD,' is a computer-based system built into all 1996 and later light-duty vehicles and trucks, as required by the Clean Air Act Amendments of 1990. So what exactly is the OBD specification, and why do we care? According to the Environmental Protection Agency's website: The information provided is only intended for reading from the OBD-II spec.

Warning! Modifying your OBD-II system to a non-certified state is considered a Federal Offense.

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