monitoring your car's health with an OBD-II display

Among the mods I've done to my car, this falls into the category of most useful and effective ones. It's not so much a mod but a simple plug and play addition - a OBD-II display gauge.

I got this multi-gauge display primarily for the coolant temperature gauge which my car does not have one. Instead it only comes with an indicator to tell if the coolant is has overheated, which usually would only come on when it is already too late.

Installation is easy, simply plug it to the OBD-II port in the car, usually found behind the dashboard under the steering wheel.

If you car was manufactured after the 2000's, high chances are it comes with an OBD-II port, which stands for OnBoard Diagnostics version 2. This port is connected to the car's ECU and is designed to make it easier to read and write to the ECU as well as pull diagnostics data. However, different manufacturers may adhere to different standards and protocols, so you will have to refer to your car's manufacturer to find out you car is compatible with which OBD-II reader.

Once plugged in, and if the device is compatible with your car, it will automatically start displaying the supported information.

There are many types of OBD-II displays on the market, most can display vehicle speed, engine RPM, coolant temperature, alternative voltage output, fuel consumption, throttle position, fault codes and a few others. Strangely though I have not yet been able to find one that displays engine vacuum reading.

But what if you car already comes with a coolant temperature gauge? It is highly likely that it is not accurate and would stick to a single reading as long as the actual temperature is under preset threshold. For example, the coolant temp gauge in your car may stay fixed on 80°c when actually the coolant temp can go as high as 100°c before the car decides to tell you something is wrong by raising the temp reading.

Case in point, see the photo below where the OBD display shows 90°c when the coolant temp gauge in my instrument cluster is still showing 80°c.

In reality, coolant temp fluctuates quickly and frequently when driving. Driving my car, it can fluctuate between 80c to 95c depending on driving conditions. My guess is, manufacturers "mellowed" the gauge so it is less distracting.

The benefit of making the actual coolant temp visible is that so you can catch any abnormal increases in the reading and perform remedy or preventative action as early as possible.

I also use the OBD-II display to show actual vehicle speed by calibrating the speed reading to match GPS readings. Some cars tend to over-report the vehicle speed - For example, my Persona's speedometer would report 100km/h when the GPS speed is only 91km/h. This is also useful if you changed your wheels and tires to a different size which would affect the speed reading - simply re-calibrate the OBD-II display using GPS speed readings.

The other handy function is the voltage reading which monitors the output of the car's alternator/generator. You can use it to ensure that the heart of your car's electrical system is in good running condition.

If you are more technically savvy and would like to pull more information from the ECU, you can get a OBD-II scanner that can connect to your phone via a physical cable, wifi or bluetooth. 

The scanner can access much more information via apps such as the popular Torque Pro mobile app. The downside being it is not as convenient or easy to install as the standalone display.

Thescreenshot below is just a handful of the many more information you can pull from the OBD-II port, all updated live while you drive.

While some non-car people may think these are superflous information that are only useful for petrolheads, truth is if you learn how to read these data, it's easy to keep track of your car's health. Even just the engine vacuum reading can tell you a lot about how well your engine is running if you know how to read the patterns (something I learned from @davidke20). This helps alert you to potential problems so you can address it before it become something more serious.