Check Engine Light

Why I haven’t blogged on this topic before now is anybody’s guess…  I get calls about this ALL the time:  You’ve probably been there – start the car up, everything is good, and then somewhere along your drive that orange Check-Engine light or Service Engine Soon light, on that orange picture of an engine lights up in the dash.  Makes your heart sink a little – am I right?


What do you do?


If I know you well enough and you call me saying “my check engine light came on – what do I do?” I may (based on your stress level) say “Well – did you check the engine?”.  I don’t use that joke often.

Or you could take the approach Homer takes from my favorate Simpsons moment:  Homer is driving down the road and he sees the check-engine light come on.  He quickly says “I thought I fixed that!” and then proceeds to pick up a piece of black tape off the floor and re-applies it over the light.


Joking aside – what do you do?  Here’s my standard answers:


First – did the light flash at you? If it did that is most dire warning the light can give you – it means your car’s computer was detecting active misfiring.  Misfiring is bad and, if not corrected, can escalate into much bigger repairs quickly.  If the light flashed, or if it is flashing now:  don’t drive the car.  Get it towed in.  The tow-charge may well become your best investment ever.

Did the light just come on / without flashing? Ok – this is a less serious warning.  BUT, we still have no idea how serious the problem is.  Back in Psychology we were taught the stages of grieving as:  Denial, Anger, Bargaining, Depression, and finally Acceptance.  I think this pattern holds true for people experiencing check-engine lights too and thus I get a lot of people working on the ‘Denial’ level.  I get questions like:  I just had it serviced or it’s due / overdue for service – is this why the light is on?  Does it come on based on some kind of mileage counter?  Sorry – no.  If your check-engine light is on your engine management system has captured a real error and is reporting it to you via this light.

If you have an active check-engine light on my advice is this:  get it checked as quickly as you can.  Try not to use the car much or drive very far.  Be aware of the car’s behavior / keep an eye on the other gauges and if you notice a change in the driving behavior get the car in quicker.  If there are obvious performance issues (hesitation, stumbling, stalling, etc) get the car towed.

Did the light come on for a little while and now it’s off? If so this is good news / it means that the active error that the engine management system was observing is now no longer active.  You should still have the car checked because the computer system will have information on this historical problem but, unless the car’s performance is somehow ‘off’, you can do this more at your convenience.  Certainly have it checked before going on a road-trip or something like that.


How do I get a check-engine light diagnosed?


One of the frustrations clients have with check-engine lights is that there isn’t really a way for the vehicle owner to judge the severity of the problem.  (With the exception of the light flashing – this always indicates a high-priority problem).  The functionality of the check-engine light is intimately tied to the vehicle’s emission systems and the EPA’s requirements for modern vehicles.  Because of this a lot of the concerns that the check-engine light comes on for are emissions related.  Some of these overlap with issues that can become or are vehicle damaging while others are exclusively emissions-only problems.  The EPA isn’t interested in having your vehicle make this distinction for you because they fear that emissions problems would get less priority.


What about free code-reading offered by parts stores?

The EPA requires that a certain level of diagnostic information be reported though a standard computer protocol that can be read by multiple diagnostic machines (computers or scanners).  This level of data (called OBDII) is easily accessed by low-cost scanners and you can get this info for free or close to free by parts stores, some lube shops, even some tire shops and other less-specialized automotive businesses.  Unfortunately the data available though this OBDII protocol is much less ‘rich’ than the computer data available though the vehicle manufacturer’s native diagnostic protocols.  The more complicated the vehicle the more true this is.  Diagnosing a modern Mercedes Benz with a check-engine light on, for example, with only OBDII information is almost impossible and the probability for an incorrect diagnostic result is very high.

Remember too – a parts store wants to sell you parts.  Providing free OBDII data to you is going to increase the likelihood of you buying parts from them.  It always saddens me to hear of someone spending hundreds of dollars on parts at a part store based on the OBDII error codes in their computer system without fixing anything.  Sometimes this process can even add to the problems.


Why should I pay for check-engine light diagnostics?


Check-engine light diagnostics does not only involve getting as much data from the vehicle’s computer as possible but it also requires a smart technician to then unravel this information, test the systems in question, and determine the real root-cause of the problem.  Factory level diagnostic computers include much richer data about what your engine and its sensors are seeing and doing / these computers can even force the vehicle to perform outputs that help a technician test your engine.

So, to get the check-engine light problem diagnosed correctly you are best to have it diagnosed with a computer that speaks your car’s native language (eg a Mercedes diagnostic computer  for a Mercedes, a Land Rover diagnostic computer for a Range Rover, etc).  The diagnostic process should additionally involve time for a good technician to then test the areas that the computer is complaining about to determine the root-cause.  Once the root-cause is found the repair is typically easy to determine and to price.

The thing to remember is this:  typically check-engine light diagnostics involve the best skills of a shop, the most expensive equipment in a shop, and the liability of ‘owning’ the results requires the shop to take on risk.  Ultimately the diagnostic part is the key part of getting your car fixed because if the diagnostics are wrong everything after that will also be wrong.


Who can best diagnose my check-engine light?


Dealers have a natural advantage:  they *should* have the best diagnostic equipment for your vehicle and should have the skills on-staff to find the root-causes.  Why do I say *should*?  Well – dealers are staffed by the same kind of people as none-dealers.  Some technicians are better than others.  If your vehicle diagnostics is handled by a senior technican (who wants to get the right answer) at a dealership the diagnostics should be correct.  When does this not happen?:  when the staffing at the dealership is lacking or the dealership determines that a junior technician is ‘good enough’ or your vehicle is less-critical to them.  Customers naturally assume that going to a dealer guarantees that the technian diagnosing their car is appropriately skilled.  Whereas outside a dealership environment a customer is going to more actively check for this competency.

A big problem with dealership diagnostics is that most vehicle manufactures ‘micro manage’ their technicians and their diagnostics processes are rigid.  Because of this the technician isn’t allowed to think for him/herself.  This results in a lot of overkill answers that ensure the problem is fixed but not necessarily in the most efficient way.  This is done to reduce the risk of wrong answers and to create a more consistent result from dealership to dealership.  BMW’s diagnostic computer, for example, includes the diagnostic tree for a given problem and the technician is required to work though the tree and then perform the repair at the end of the tree.

Another dealership problem:  do they care about or even know your vehicle anymore?  I get odd-ball cars all the time that the owner just didn’t feel good about how the dealer was approaching the problem.  Dealership techs would much rather work on their run-of-the-mill vehicles than the unusual ones that they don’t know well.  This is especially true for older vehicles outside of warranty – the technician has no guarantee that he/she will get any work from his/her diagnostic process because it has to be sold to the vehicle owner.  Additionally if the dealership doesn’t see a lot of value in the relationship with the vehicle owner then that vehicle will be lower priority.

Independent Specialists:


Your best choice for diagnosing your check-engine light is an independent shop with the equipment and competency to diagnose your problem.  The potential dealership problems above are usually not present in a speciality shop where the shop wants to build a relationship with you.  But, of equal important is the shop’s integrity so that you won’t be oversold or otherwise decieved.

How do you determine if the shop is appropriately equipped – ask this question:  Can you update my vehicle’s software with the latest updates from the manufacturer? You may or may not need this service but only the best shops can 1 – do it and 2 – have the confidence to say they can.

The question of integrity is more difficult to answer – I would suggest you start with a referral from a trusted friend where you can.  Also do some internet searching and see what the shop’s customers say.  Understand that nobody is perfect and typically upset customers are more vocal than happy ones but if you do some internet searches and reading you’ll sense a trend.


Final Thought:


People forget this but it’s critical:  don’t shop-hop.  Build a relationship with a good shop and stick with them.  Even if on some repairs they seem higher in price than what you think the going rate should be.  A good shop is like a good family doctor – they will know your car and they will know you.  Your family doctor is much better at helping you than the one at an insta-care that doesn’t know you or your history.  Your best opportunities for saving in auto service is, like in medicine, to catch things early.  A good family-mechanic will help you do this.  Look for this in a shop:  good service history records and the ability to retrieve them is key and demonstrates a more managed business.  It shocks me but I still see hand-written service invoices from some shops.  Consider this:  If the shop is that far behind the times in invoicing – where their money is – what else have they fallen behind in?  A shop that values an on-going relationship with you is your best weapon in any battles with your vehicle for a check-engine light or any other problem.