Backyard diagnostics
ON-BOARD SCANNERS DON’T HAVE ALL THE ANSWERS
Over the years there have been an increasing number of consumer devices capable of communicating with a vehicle’s On-Board Diagnostic (OBD) system.
These used to be simple handheld devices used to receive fault codes and other information about the car’s general health. Engine management systems have increased in complexity with technology such as “fly by wire” accelerator systems, and advanced high pressure fuel delivery technology.
Automotive technicians today have adapted their knowledge to have a greater understanding of engine management systems and the correlation and interactions of the different componentry that make up engines controls.
It is through training and experience that technicians have the ability to diagnose a faulty part.
With this in mind, we decided to do some myth-busting on an over-the-counter OBD scan tool. These are becoming more commonly found in retailers, promoted as an item that’ll diagnose automotive problems without having to visit a mechanic.
The particular scanner we looked at came with a disclaimer saying that it was “vehicle dependent” and able only to “interpret the data that your car provides”.
This is an instant red flag, as it wipes the seller’s responsibility for not necessarily being able to provide all the information you need.
For example, if the scanner provided fault codes for crankshaft and camshaft position sensors, you might assume that you have two faulty sensors.
Replacing these isn’t a cheap exercise, and to later find a skipped tooth on your timing belt would cause some frustration to say the least. A good technician would recognise that it would be unlikely for both sensors to fail simultaneously and understand that the sensors’ position and reading are affected by a vehicle’s timing.
We then ran into a little bit of trouble with the instructions that recommended we jail break our Apple device or purchase additional software. We determined that this was too risky and costly, so we opted to download one of the many generic scanner software applications, available for free in the Apple app store.
The device operated exclusively with the Engine Control Unit (ECU), so other systems such as airbag units or ABS brakes could not be assessed. The scanner allows you to read engine fault codes and clear them from the ECU’s memory. It also allows you to monitor other inputs such as engine rpm, air flow and fuel pressure. If you had detailed information from the vehicle manufacturer, and were a highly skilled hobby mechanic, this could help you narrow down a fault, but using live engine data, even for a skilled technician, can be difficult.
We decided to introduce a fault by disconnecting the cylinder one coil on a 2017 Volkswagen Tiguan.
As expected, the engine light came on stating the scanner had detected a failure. We read the code and it correctly identified a cylinder one misfire. After reconnecting the coil we were able to clear the fault code and restart without its warning light on.
Although it correctly identified a fault with cylinder one, there are dozens of potential reasons for a cylinder failure and without further investigation you could empty your wallet on new spark plugs, a coil or an injector before finding out it was a broken wire or in this case, simply a loose connection.
OBD tools like the one we tested often claim to be an answer to prayers, offering to save customers thousands.
It sounds great, but knowledge is a dangerous thing in inexperienced hands. If scanners had all the answers, the life of a technician would be breezy.