Wild guesses do not fix cars.

Brockles — Tue, 20 Mar 2012 06:28:53 -0800

Automotive questions generally, but specifically those that mention a Check Engine Light, repeatedly get flooded with well-meaning but ultimately pointless (and often directly unhelpful) anecdata about their own check engine light experience in their own (similar or completely different) cars. It is in the best interests of Askme if that kind of thing just stopped. The question that finally brought this to a head is this one, but this is extremely common (almost to being standard form) and I find it very frustrating and it has to be confusing for the asker. They get lots of stuff that seems like 'information' and almost none of it is at all relevant. Knowing that a CEL is on is not even close to being able to guess at a cause of the problem. To use an analogy, imagine a tech support person reading a forum and seeing the following: OP: "I have a windows machine and an error window came up - is this a major problem or can I ignore it" Then, while one lone voice says "What did the error window actually say?" the rest of the thread is filled with people saying "when my mac had an error message it was because my internet connection was down" and "My error message was on a Windows machine like yours and it was because my printer had run out of ink - just ignore it" or "My error message was because I had a virus - YOU PROBABLY HAVE A VIRUS OMG" or "My error message was because my email account couldn't check messages - maybe you've been hacked? Change all your passwords just in case". That's a pretty apt analogy in the vagueness of 'error box' and CEL and and it's kind of amusing now that i read it back. But it is exactly what happens in automotive questions. It is borne of people desperately wanting to answer questions in a helpful way but it needs to be said that this kind of anecdotal rubbish is directly and explicitly unhelpful and people should be more aware of this and knock it off. In the interests of getting people to understand precisely what they are posting, I'll try and explain why it is unhelpful and pointless. It doesn't help the OP at all, which is the prime purpose of AskMe. The check engine light is not something you can use to diagnose a problem. On its own it doesn't actually tell you ANYTHING AT ALL. Consequently because you had a check engine light on in your own car and later a problem was found does not imply any kind of direct cause and effect that can be extrapolated backwards. Your anecdote about your own check engine light is likely of zero use in everything other than blind luck that this is miraculously the same issue. Even worse, implying that a CEL can mean a particular fault without further investigation is directly damaging and is likely to cause the OP to make a badly informed decision. If you don't know that a CEL is not enough for even a vague diagnosis then you don't understand it and should refrain from making wild guesses. In the nicest possible way it doesn't matter ONE LITTLE BIT what caused your own engine light, even if it is the same model of car, unless you know for a fact it was the exact same trouble codes. Even then, the same trouble codes can mean three or four likely causes. To repeat, The CEL is NOT a symptom. It never is. You can assume precisely nothing from knowing the CEL is on. If you think you can, you are wrong. It is just a light to signify that the ECU has detected symptoms and they need reading and understanding with a code checker. The check engine light is triggered by a significant number of sensors and parameters and produces many conclusions from serious to irrelevant (emissions ECL triggers I am looking at you) and it really is no help other than 'there's something you need to look at'. 90% of these conclusions cause the ECU to determine that something needs further investigation and so it illuminates the CEL - the 'please take me to someone that can look at this and see what needs fixing' light. It is a very complex system with a very limited means of transmitting to the owner that it needs investigating. The fact that it uses a single light for everything does not mean that it is a small variety of potential issues being indicated. Only with the codes supplied from the ECU when a CEL is triggered can anyone possibly make any sort of educated guess as to the cause and if anyone tries, they are being anything from directly unhelpful to just adding noise. Even then, a code can often only produce a system error of several components and the system then needs to be checked over. Evap system codes is often the fuel cap, for instance, but not always as other component failures produce the same code. This is a very common 'answer' - "My ECL was the fuel cap - check that!". It's just.... pointless noise. There are very few CEL codes that produce a direct fault, so that code 11356 means that component X is wrong. So in short, please do stop doing this. It is rare that any Askme posts enough information for a diagnosis in most automotive threads anyway (a lot of my answers will suggest several causes and means to narrow them down for this reason) and wild and uninformed guesses are a problem in almost every single one but at the very least a greater understanding of the CEL would start to help askers and answerers alike. The sheer volume of noise in automotive threads drives me nuts and hopefully if awareness is raised of the problems of this kind of answer then at least some people will get it. At the very least, linking to this metatalk thread in questions where this is starting to happen may at least quell it a little. Ok. I have taken a deep breath now.

MetaTalk posts tagged with checkenginelight

Wild guesses do not fix cars.