7 Tips For Success With Fault Codes

Johnny’s Top Seven Tips For Success

Arrann Diamond

Automotive Information

As you may know I’m a huge fan of process. Wherever you find success you’ll be sure to find a well devised system along with a tried and tested process that has paved the way to glory. This has never been more evident than within our world of fault finding, which is why the Auto iQ 15 step diagnostic circle sets out the system for repeatable success when it comes to the more technical repairs that cross your thresholds.


Whilst I’d love to wax lyrical on all 15 steps, there just isn’t the space in a single article, so with that in mind I figured we’d delve into at a subject that’s often overlooked and rarely covered when “talking technical” and that’s fault codes.


"What!" I hear you cry. “An article on pulling codes?”, “Really?” “Surely it’s just plug it in and away we go?”

Not quite.

And here’s our top seven tips on what, and what not to do to ensure that you make the most of this step in your diagnostic process.

Success With Fault Codes

Johnny’s Top Seven Tips for Fault Code Success...

1. Select the right tool

Using a generic scan tool has its place but if you truly want to be effective and profit from this type of work then select the manufacturer tool. I switched to using manufacturer tools and information many years ago and it enabled our garage to get ahead of the competition.

Using the right serial tool will give you buckets of confidence and you’ll often get additional information as part of the fault code that a generic tool won’t supply. Not only that but it’ll remove that anxious feeling that so often blights our day as we think “will this scan tool communicate”.

2. Carry out a global scan

Effective diagnosis is about gathering as much information as possible. The more information you have the more informed your decision making process will be. Reading just the  codes in the system you perceive to be faulty will only ever lead to extended diagnosis time in the long run.

We’ve seen non start faults caused by air bag systems, inoperative infotainment caused by energy management systems, drivability faults caused by A.B.S systems, the list just goes on and on. It really is quite common to see faults in seemingly unrelated systems causing havoc on a vehicle. You’ll give yourself the best chance of reducing your diagnostic time when you look at the complete picture by carrying out a global scan.

Wherever you find success you’ll be sure to find a well devised system along with a tried and tested process that has paved the way to glory.

3. Document the details

Writing the fault code down is a given, but so often there’s additional data that can be used to fill in the gaps as part of the puzzle.

Noting the whole code is often a benefit for example P2294 is a code for a fuel control valve on a GDi Golf we worked on recently, noting the full code of P2294-004 will often pay dividends when it comes to looking for causes of any given fault code. It’s the small details that count.

It’s also worth taking note of other associated data such as whether the code is sporadic or permanent. Freeze frame data can also be worth its weight in gold indicating many physical parameters for when the code was raised. Using this information to recreate the scenario when the code was initially raised can often reduce your diagnostic time dramatically.


I know it’s tempting just to see which ones bounce back but you’ll be causing yourself a whole bunch of hardship.

Many systems will reset the learned parameters (adaptations) which will remove any diagnostic clues waiting to be revealed when you look at serial data. This is trebly important when looking at engine management and drivability faults. The last thing you want to reset is fuel trim data and lose that diagnostic gold dust.

There are of course some instances when you’ll want to clear them straight away but that’s a whole other conversation for a different day.

5. Don’t ignore OBD

OBD is often perceived as the poor relation of the manufacturer’s software, but in reality there’s a wealth of information here that you’ll not want to brush aside.

Not only that but on some vehicles you’ll not be able to clear the MIL light until a fault code reset has been carried out in both the manufacturer and OBD programs.

At Auto iQ fault codes only make up 6% of our diagnostic process.

6. DON’T Ever

Don’t ever change a part based on the code! A code is raised once a monitored parameter steps outside of a given tolerance, and there are so many reasons that any one code can be raised.

Now, there’s a bunch of variables that’ll change the probability of a given fault being the components itself, but even for a common temperature sensor fault code there’s only a 12.5% chance of it being the sensor once all the other options are taken into consideration.

7. Just 6%

Understand what part codes play –  Points one through six are important and essential in an efficient and profitable diagnosis, but it’s crucial to understand the part fault codes play in the WHOLE diagnostic process.

At Auto iQ fault codes only make up 6% of our diagnostic process, which is a fact worth bearing in mind the next time you come to make a decision based only on the code 🙂

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