Mode Six Onboard Test Results is the OBD-II service that reports the detailed outcomes of the self-tests your engine computer runs on emissions systems. Instead of a simple pass or fail, it shows the measured test value alongside the minimum and maximum limits the computer used to judge it. For a DIYer, this service can … Read more
Mode Four clear codes is the OBD-II service a scan tool uses when you press erase or clear. It looks like a simple delete button, but the request removes much more than the trouble codes on the screen, and understanding its full reach prevents costly diagnostic mistakes. This article examines the service itself: the data … Read more
Mode Three stored codes are the confirmed emissions-related trouble codes that a scan tool retrieves when it asks the engine computer for its fault list. When a code reader shows the codes behind a lit check engine lamp, it is almost always using this service. OBD-II defines ten standard diagnostic services, often called modes and … Read more
Mode Two Freeze Frame is the OBD-II diagnostic service a scan tool uses to request the snapshot of engine conditions stored when an emissions-related trouble code set. Where freeze frame data is the information itself, Mode 02 is the standardized request and response that brings that information out of the engine computer and onto your … Read more
Mode One Live Data is the OBD-II diagnostic service that lets a scan tool read the engine computer’s current values while the vehicle is running. Engine speed, coolant temperature, fuel trims, oxygen sensor readings, and many other parameters appear on your screen and update continuously. Most owners use this service without knowing its name, simply … Read more
Professional diagnostic scanners are advanced tools used by repair shops and experienced technicians to communicate with nearly every computer module in a vehicle, not only the engine computer. They go far beyond reading generic codes, adding component tests, service procedures, and detailed data analysis. This guide explains what these scanners can do, how they differ … Read more
OBD II code readers are compact diagnostic tools that plug into a vehicle’s 16-pin diagnostic port and retrieve stored trouble codes from the engine computer. They are the most common first step owners take when the check engine light comes on, and many cost far less than a professional scanner. This article explains what a … Read more
J1850 communication protocols are two related SAE standards, known as PWM and VPW, that many domestic OBD-II vehicles from the late 1990s and early 2000s use to send diagnostic data to a scan tool. Both appear on the approved OBD-II protocol list, yet they work differently at the wire level. This guide explains how the … Read more
The KWP2000 protocol, short for Keyword Protocol 2000 and defined as ISO 14230, is a diagnostic communication standard used on many OBD-II vehicles built during the early and mid-2000s. It shares the K-line with ISO 9141-2 but adds faster start-up and a richer set of diagnostic services. This article explains how KWP2000 works at the … Read more
The ISO 9141 protocol is a serial communication method that many OBD-II vehicles from the late 1990s and early 2000s use to exchange diagnostic data with a scan tool. Its OBD-II version, ISO 9141-2, runs over a single data line in the diagnostic connector. If you own or work on an older vehicle, understanding this … Read more