Why you need an OBD2 scanner tool when towing

Did you know a $50 gizmo about the size of a matchbox, DIY-installed with no tools, can prevent thousands of dollars of damage to your tow vehicle?

Here's everything you need to know about an OBD2 scan tool, and why you should probably get one before your next big trip...

Hauling a caravan around can put extra strain on your tow vehicle's engine and transmission which can eventually lead to premature wear and failure. So monitoring the vitals of your drivetrain and even modifying your driving accordingly, can go a long way to protecting your investment as well as prevent being stranded on the side of the road.

Modern, and even not-so-modern vehicles are full of sensors and computers that capture very useful live data, often not visible through your dashboard displays. Fortunately, an OBD2 scanner can give you access to this data.

Some of these scan tools display data through third-party phone apps, while more sophisticated models utilise dedicated display modules.

OBD2 scanners can also be used to understand and reset fault codes, which can be a real lifesaver if you're in the middle of nowhere...

OBD2 stands for On-Board Diagnostics, version 2. Since the mid-2000s, every new vehicle sold in Australia comes with an OBD2 port – a small, trapezoid-shaped socket usually hidden under the dashboard near the steering wheel.

Basically, an OBD2 scanner is an electronic device that plugs into this port and accesses data from your onboard sensors and computers. Mechanics have been using sophisticated scan tools to gather data and diagnose faults for some time, but it's only recently that affordable scan tools have been readily accessible for anyone to use.

A great thing about the basic DIY units is they're almost universal, so you don’t have to worry about selecting a car brand/model-specific unit. If you have the port in the car, the scan tool should work (although some vehicles provide less data than others without special programming.) And if you change your car, you can keep using the same tool.

It’s also good to know that fitting a scanner is not a modification; it's simply a device that you plug in or unplug. Also, a regular scan tool doesn't change any performance characteristics. Importantly, it would be hard to argue that a reputable scanner could compromise your car warranty. One caveat could be clearing codes – more on that later.

When your tow vehicle is working hard, it gets hot, and overheating can be a car killer.

Sure, all cars will show some form of engine temperature readout on the dashboard. Additional data that may not be visible to you without an OBD2 scan tool includes automatic transmission temperature, accurate engine coolant temperature and exhaust gas temperature.

To be fair, some vehicles do display some of this extra data through the dashboard, but plenty don’t.

First up you need to know what the normal operating heat parameters should be. You can learn this by either keeping an eye on the numbers under easy driving conditions, or by getting advice on an online car forum.

Then it’s up to you to be alert to temperatures creeping over. Some tools/apps allow you to program upper limits that will trigger an alarm if they're exceeded.

Interventions for overheating can include stopping, slowing down, driving in a different gear or checking your cooling systems.

A scan tool can also tell you other things about what’s going on in your car. You can see what gear the automatic transmission is in as it shifts up and down. So a car that sits in top gear may cause transmission overheating when towing. If you can see that happening, you can switch to manual mode and lock the transmission into a lower gear.

Seeing turbo boost pressure can also tell give you an idea of how hard the engine is working on long climbs. Diesel Particulate Filter (DPF) status helps you know when a regeneration cycle is happening, so you don’t shut the engine down mid-burn. And battery/charging system voltage readings can help you know if your alternator is keeping up. This is all helpful if your 'van is running a DC to DC charger.

As standard, when the sensors and computers in your car detect a problem, warning lights/messages are activated on the dashboard. The car may even go into limp mode to protect itself from critical damage.

The car’s computer logs a Diagnostic Trouble Code internally, but this is not visible through the dashboard. An OBD2 provides access to the DTCs describing the problem and giving you the option to clear it. Understanding the problem provides a better chance of making a fix out in the field.

If you're confident that you have resolved the problem, you may choose to clear the fault. However, caution should be exercised as you may be failing to address a major problem. And you're removing diagnostic information that a mechanic may find useful later on.

OBD2 scanners come in a few main types:

Basic handheld units

These are small, plug-in tools with their own screen. They're great for reading and clearing codes, but they aren't so useful for caravanners looking to access live data.

Bluetooth/Wi-Fi dongles

These plug into the port and pair with your smartphone or tablet. Using a free or inexpensive app, you can then create a custom dashboard of gauges.

They're a cost-effective method of accessing live data, but can require some tech-nerd skills to fully set up. Another downside is when you use your phone/head unit for something else, you can’t see the data.

Dedicated OBD displays

You can also buy a unit that mounts permanently on your dash with its own display. They're a little more expensive and add clutter to your dashboard, but they always display the data. They're also less fiddly to set up than the dongles that pair with phones.

Our 'guinea pig' for a good sample installation was a MY24 Isuzu D-MAX ute. Despite being a popular, modern tow vehicle, it fails to display some very useful data.

We purchased a Veepeak OBD2Check BLE+ ($56) and Car Scanner Pro ($13) and used an Apple iPhone. We were able to access a wealth of data by using menu driven options without any special coding.

However, results will vary with other vehicle and set-ups. There are many comparable devices and apps available that do similar jobs through iOS and Android, so it pays to shop around.

Here is an overview of the process...

Related: Top-5 en route emergency gadgets

Related: Top-10 RV emergency items

Related: Buying a dash cam for RV touring