Everything you needed to know about OBD2

ByWes WhitworthJune 11, 2020
Everything you needed to know about OBD2

If you’ve got a car or four-wheel drive built after about 1994, chances are you’ll have an OBD2 port (On-Board Diagnostics Ver.2 port). They’re often up under the steering column, and sometimes over in a kick panel, but it’s not so much its location (if you need to, check out your owner’s manual to find it) but what it can tell us that’s important.

The OBD2 port is an outlet from the ECU (Engine Control Unit – essentially the vehicle’s brain) that will give you access to both the data the ECU is receiving from sensors and also any Diagnostic Trouble Codes (DTC) that the ECU is putting out.

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OBD2 port location on a 2017 HiLux

But what is a Diagnostic Trouble Code (DTC)?

If you’ve ever had the engine light come on, or all of the lights start randomly popping up on the dash like a Christmas tree, chances are the ECU is getting information from a sensor that it doesn’t like, or is outside what it knows to be normal.

From there, the ECU will usually drop the vehicle into limp mode which, more often than not, will force you to head in to a dealer or have the car towed to a mechanic who can diagnose, find and resolve the issue.

What can an OBD2 port tell you?

This is where things get interesting. You see, the OBD2 port can tell you everything that the sensors throughout your vehicle are reading; far more than just things that will cause a light to ping up on the dash such as the ABS light, check engine light and so on. If there’s a sensor attached to a part of your tow rig, you can read and interpret the data that that sensor is sending to the ECU through the OBD2 port.

To be able to read the signal and data coming out of an OBD2 port, you’ll then need a reader of some description. There are a bunch on the market – I run a ScanGauge 2 (you’ll find a review we did on it in Unsealed 4X4, here) and it gives me access to all of the data the OBD2 port has available. This includes all of the data coming from the onboard sensors, from an EGT and DPF loading value that the DPF sensors give (on the 1GD-FTV HiLux anyway), to RPM, engine load, water temp, intake temp, boost pressures and voltage. So there are more data-based sensors than you’ll know what to do with.

In addition, there are also the error codes. For example, the ABS sensors; if they are sending data (or not sending anything at all) to the ECU outside of normal parameters, you’ll often get a dash light (or multiple lights like the aforementioned seasonal festive greenery) to tell you something’s wrong. Where the OBD2 port comes in handy is it will be able to read what the error is, and let you know exactly where the issue lies. You’ll get a code in a specific format that you can decipher, or Google the code, to find out what the issue is.

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The OBD2 port can tell you more than just problems, it can display all readable sensor data, depending on the gauge you use.

What Diagnostic Trouble Codes mean, and how to interpret them

Besides being a scary code that will most likely mean nothing to you when it shows up on a scan tool or laptop, your DTCs are actually pretty easy to work out. First thing you’ll need to know is the letter at the start. This will tell you where the error is – B for body, C for Chassis, P for powertrain (engine/drivetrain) and U for user network (Canbus, Wiring system, UART, etc.).

The next number will tell you if it’s a generic code or a vehicle-specific code. Bear in mind most codes you will see will relate to generic codes, unless your vehicle manufacturer ran out of generic codes to use – 0 is for generic codes and 1 is for manufacturer-specific codes.

The third number or letter in the error code gives you an indication of where the issue has occurred. With 1 being Fuel and Air metering, 2 being the injector circuit, 3 being the ignition system/misfire, 4 being auxiliary emission controls (think DPF/EGR), 5 being vehicle speed control and idle control circuit, 6 being computer output circuit, and 7, 8 and 9 being driveline – gearbox, transfer case, diffs, etc. A, B and C relate to hybrid/electric vehicle systems (not yet so common), so chances are when the Rivian, Tesla and other EVs start turning up Down Under we’ll start seeing these codes as well.

Finally, the last two characters in the DTC give you the actual fault description; you’ll most likely need to Google it to find out what it is; we could have pages and pages and pages on the different codes here, but we’re trying to keep this short, and sweet.


The TLDR; have a look at this diagram above, it’ll help you work out the codes and is a good place to start looking if you don’t have access to the interwebs to look it up. It’s probably a wise idea to screenshot this so you’ve got a copy of it stuck in your photos on your phone.