ENGINE Fault Code Readers

Many of us dread the sight of the engine management light, or to give it the official title, malfunction indicator light (MIL). Perhaps it’s the fear of the unknown or being alerted to a problem that may not seem to be affecting the running of the engine. However, it’s much easier to take a more positive attitude and find out what all the fuss is about, as it may be something or nothing, and that’s where a Fault Code Reader (FCR) can come to the rescue. They were once a dark art, consisting of expensive diagnostic equipment that only a professional garage could afford, which consequently entailed a fifty quid fee to plug it in and decipher the problem, if there was one. Nowadays, there are many cheaper solutions, and one of them is to buy your own fault code reader - but are they any good?

To answer this question, it’s essential to know a little about how fault codes work and the history of this subject. It all dates back to the nineties when ECUs and diagnostics were gathering pace. Many manufacturers developed their own means of plugging in specific diagnostic equipment to their vehicles, so there was no standard method of connection. An American derived standard consisting of a 16-pin plug/socket was developed, which we now know as OBDII. The European equivalent is EOBD (see the Jargon Buster on page 38 for abbreviation definitions). Whilst the means of connection had been standardised, the programming languages used by the various ECUs (also known as protocols as they are a means of communication) needed standardising, and there are a few of them, such as KWP, PWM and VPW. Furthermore, a standard became established for faults, which we now call fault codes or diagnostic trouble codes (DTC - see the separate information on this on page 37).

Deeper diagnostics

So with everything standardised, it helped to open up the market for making generic fault code readers that could communicate with most vehicles with an OBDII/EOBD connector. Car makers still use their own manufacturer-specific fault codes, some of which can be retrieved by the fault code readers we’ve tested, and this should provide a deeper level of diagnostics along with viewing live data to see whether any sensors are displaying abnormal readings. And it’s perhaps this latter point that needs to be considered when diagnosing problems because not all of them can be identified by the ECU to raise a fault code, so monitoring live or recorded data (freeze-frame) is often the solution, which is more involved than retrieving a fault code and hoping it will give you the answer as to why there’s a problem.

The cost of fault code readers varies greatly, along with the different types. One of the cheapest is a £10 plug-in Bluetooth dongle that can send data to a laptop and be interpreted by free diagnostic software. We decided to concentrate on the handheld devices that generally cost from around £30 upwards. We only wanted to look at being able to read engine fault codes, but the more you pay, the more features you get, such as being able to switch off