Fault codes and conspiracy

I was hearing about some chap who ran his car on Biodiesel and had a few engine problems, the engine would loose power and display the legendary ‘Check Engine’ light prompting him to take it to a dealer to have the fault codes read. There were many fault codes set, mainly due to various blockages, which lead the dealer to change a number of expensive components that in truth were perfectly ok. His conclusion was that

The check engine light, lack of knowledge can lead to bad interpretation and expense.

manufacturers must design the fault detection system to generate revenue from needless parts sales, this is of course complete cobblers, not least because manufacturers always loose heavily when any part is changed under warranty. But also bear in mind that thousands of us Engineers work developing these systems and on the whole we are not a bunch of psychopathic con artists with a hatred of the driving public! On the contrary, most of us are car enthusiasts and obsessed with doing thing right.

So how did this bloke end up in that situation, and what strange sequence of events led him to his disparaging conclusion?

Well, Biodiesel made to BS 14214 contains a fairly high amount of solvents which can cause issues

in cars that have run on ordinary diesel for some time. Wax and other deposits can build up a bit like those fatty deposits you get inside dishwasher drains, but the solvents in biodiesel clean out the tank and fuel lines causing the debris to float off and block the fuel filter (which is only doing its job). Common practice when deciding to run on biodiesel is to fit a new filter first, run the car for a short time to flush things through and then fit another filter; they generally cost only a few pounds. But on this car that wasn’t done and the fuel flow became restricted so when the demand was high the engine would loose fuel pressure and reduce the power level to compensate, to the driver the car drove normally until accelerating hard to overtake when it would suddenly loose power.

Be careful what you put in the tank, cheap fuel can cause expensive repairs.

A fuel pressure fault would be flagged but international fault code listings are, by their very nature, quite generic which works well for most problems, but in this example the system would only be able to detect that the fuel system pressure had dropped as the demand increased when he was overtaking. As soon as the engine had been restarted the pressure would return.

Once the engine has been restarted a few times the system must assume the fault has been repaired, as there are big penalties for manufacturers if their cars keep flagging false warnings, and so by the time the diagnostics tool was plugged in the codes may have been cleared automatically. So when our chap went to the dealer there would be no trace of the fault code for de-rating, just some ones about fuel pressure which lead to the dealer mistakenly replacing the fuel pump at great expense which obviously would not cure the blocked filter. The customer took the car away and unsurprisingly the same problem occurred, so he took it back to the dealer.

In this case the dealer stated that as well as the generic codes there are manufacturer specific codes that can only be read by the manufacturers own diagnostic equipment, so the system was hiding information and it wasn’t their fault. This is unfortunately what started the conspiracy theory!

Manufactureres spen millions testing engines in all conditions to eradicate faults.

Manufacturer-specific fault codes are there as an extra layer of sophistication and reflect aspects of the engine system design that are unique to that manufacturer and that particular type of engine. They are even more open to misinterpretation which is why car companies are keen to only give them to people who have been properly trained. So yes; there is a separate fault list, but it’s not some secret conspiracy, just a reflection of the very high complexity of modern control systems.

It could well be that the garage personnel had difficulty understanding the diagnostics which is entirely understandable as the systems are hugely complex and every car is different. Not only that, but the technology is changing all the time, so having an understanding of common systems available five years ago is of very little use on cars of today. This complexity is driven by emissions legislation, safety requirements and customer demands whilst reducing costs, it is done out of necessity. Modern engine management is one of the most complex and demanding control systems commercially produced, and yet this feat is hardly recognised, which is a shame.

Its complicated enough without conspiracy theories.

So the moral of the story is two fold; there is a skill to interpreting fault codes and they need to be used in conjunction with traditional fault diagnostic techniques (ie: if there is not enough fuel getting through, check for blockages!), and manufacturers don’t design in faults deliberately, it’s hard enough as it is!

Advertisements

About Ralph Hosier

I love exploring everything the world has to offer, the fabulous beauty and intricacies of nature, the stunning majesty and grandeur of the universe, and the fascinating range of chocolates available from the local sweety shop. I have led a charmed life, sure there has been extremes, but the highs far outweigh the lows. I get paid for arsing about in very fast cars, I get to write about them and amazingly get paid for this too. My days are usually filled by making prototype and concept cars for car companies, a dream job. I have lived many of my dreams, worked all over the world, raced cars built by my own hand (and hardly ever crashed really badly), seen things and done stuff. But nothing compares to the love of Diana and my son Peter, beyond my greatest hopes. I am a chartered engineer, a member of the Institute of the Motor Industry (IMI), and of the Institute of Engineering and Technology (IET) and I am a member of the Guild of Motoring Writers. A pleasing fact is that there are now more letters after my name than there are in it ;) R.Hosier B.Eng(Hons) C.Eng MIET MIMI MGoMW
This entry was posted in Car industry uncovered, Technology Explained. and tagged , , , . Bookmark the permalink.

One Response to Fault codes and conspiracy

  1. Danny Smith says:

    Really interesting post. It’s all valuable info to the layman, and I couldn’t agree more with the conclusion. I have found that diagnostics systems have, in some cases, lead to a garages reliance on the computer. In my case persistent misfire (bear in mind my lack of mechanical knowledge) led to repeat visits to my local vehicle specialist, racking up labour hand over fist. I eventually got sick of their expensive inability to diagnose the problem and took it to PowerStation, who took the traditional diagnostics method, then walked me through what they had done and what had happened. Turns out the original garage cracked a sparkplug in a service. So, while garages need to consider all the fault-finding options, we as customers also need to exercise some sense and make sure that garages are approaching problems in an appropriate way. If not – vote with your feet (wheels?) and find a garage that operates in a sensible way. A garage that isn’t willing to discuss their approach probably isn’t the best place for your pride and joy!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s