Check Engine Light
Thread Starter
Joined: Sep 2008
Posts: 1
Check Engine Light
I have a 2000 Mercedes 320 with roughly 128k miles. My check engine light came on and was wondering if it could be more for informational purposes or something could actually be wrong? I have been on time for all my oil changes and regular maintenance.
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Joined: Dec 2004
Posts: 2,410
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RE: Check Engine Light
Feeling extra helpful this morning but wonder why you haven't searched the forum for the answer to your question.
The illumination of the yellow "Check Engine Light" (CEL)means that SOMETHING that threatens emissions (legal rewquirement) has occurred and that the engine needs to be checked.
When the CEL illuminates its sets diagnostic codes (DTC's) that assist in determining what has occurred. this process is known as On Board Diagnostics (OBD) and since about 1996 in the States and approx 2000 in Europe ALL cars have had to comply with the standard known as OBDII.
Since about 2000 (dependent upon make, model etc the engine computer (ECU) also records the engine conditions present at the very moment that the code that caused the CEL to illuminate occurred.
Codes do not always immediately illuminate the CEL. Some do, some don't dependent upon severity. If less severe then a number of instances of an occurrences of the code may need to take place before being elevated to a level where the CEL is illuminated.
If the CEL is ON the vehicle will not pass its annual SMOG / MOT or similar test since by definition there is something wrong with respect to legal emission compliance.
Next step is to get the DTC's read, recorded and reset.
The codes can then be analysed and the likely cause isolated.
If you post the DTC;s here we will endeavour to advise what needs to be done. Some places in the States will read the codes for free, However there is often a charge. If you are charged insist on a written report (computer generated) so that you can be sure that the faults reported are genuine and associated with your vehicle.
The Mercedes Benz Star system SDS carries out a comprehensive check of all 12+ on board computers and records the status of each with appropriate pending and set codes with general vehicle details listed at the top. Chassis No., Mileage, Date etc etc.
Whilst seeking advice on what the codes mean determine whether the CEL returns. i.e. the fault continues.
In some cases the CEL may be illuminated CORRECTLY but only under specific severe conditions that may not be readily repeated. in which case take the illumination of the CEL as a WARNING and that something somewhere is nearing end of life and will require replacement at some point in the future or at least when the specific conditions are repeated.
There seems to be a misconception that sometimes the CEL comes on for no reason. i.e. the CEL system is defective. Whereas this is possible you should have confidence that if the CEL has illuminated then something WAS NOT CORRECT at the moment in time that the CEL illuminated. It means a code has been set.
If no code is present then that is problematic.
However many people find that just resetting (cancelling) the CE/DTCL is all that is required since the conditions that caused the CEL to illuminate were unusual and unlikely to be repeated. They conclude that the CEL illumination was spurious and in error. This is not normally the case,.
A good example is a misfire. As the driver you may be totally unaware of this condition were it not for the CEL. The system is far more sensitive than the driver.
The CEL may illuminate after a particularly heavy and unusual (for you) acceleration. The engine misfired under this TRANSIENT condition and set the CEL/ codes. However after resetting the CEL you may find that unless you repeat the severe acceleration that everything seems to have returned to normal. This is why the computer saves the conditions prevailing when the CEL was set.
The computer senses every single misfire (its that sensitive) but does not set the CEL until a pattern or a set number of misfires (individual firing stroke) has been reached. An occasional random misfire is to be expected and for this reason the computer filters out such activity below a set threshold value.
Hope this makes sense and clarifies the situation for you.
Get the codes read, recorded, reset the CEL and come back with the findings.
Don't go throwing money at the vehicle with a tune up, new plugs and filters etc unless these are overdue for change anyway UNTIL you have determined what codes have been set and whether the CEL returns.
Stuart
The illumination of the yellow "Check Engine Light" (CEL)means that SOMETHING that threatens emissions (legal rewquirement) has occurred and that the engine needs to be checked.
When the CEL illuminates its sets diagnostic codes (DTC's) that assist in determining what has occurred. this process is known as On Board Diagnostics (OBD) and since about 1996 in the States and approx 2000 in Europe ALL cars have had to comply with the standard known as OBDII.
Since about 2000 (dependent upon make, model etc the engine computer (ECU) also records the engine conditions present at the very moment that the code that caused the CEL to illuminate occurred.
Codes do not always immediately illuminate the CEL. Some do, some don't dependent upon severity. If less severe then a number of instances of an occurrences of the code may need to take place before being elevated to a level where the CEL is illuminated.
If the CEL is ON the vehicle will not pass its annual SMOG / MOT or similar test since by definition there is something wrong with respect to legal emission compliance.
Next step is to get the DTC's read, recorded and reset.
The codes can then be analysed and the likely cause isolated.
If you post the DTC;s here we will endeavour to advise what needs to be done. Some places in the States will read the codes for free, However there is often a charge. If you are charged insist on a written report (computer generated) so that you can be sure that the faults reported are genuine and associated with your vehicle.
The Mercedes Benz Star system SDS carries out a comprehensive check of all 12+ on board computers and records the status of each with appropriate pending and set codes with general vehicle details listed at the top. Chassis No., Mileage, Date etc etc.
Whilst seeking advice on what the codes mean determine whether the CEL returns. i.e. the fault continues.
In some cases the CEL may be illuminated CORRECTLY but only under specific severe conditions that may not be readily repeated. in which case take the illumination of the CEL as a WARNING and that something somewhere is nearing end of life and will require replacement at some point in the future or at least when the specific conditions are repeated.
There seems to be a misconception that sometimes the CEL comes on for no reason. i.e. the CEL system is defective. Whereas this is possible you should have confidence that if the CEL has illuminated then something WAS NOT CORRECT at the moment in time that the CEL illuminated. It means a code has been set.
If no code is present then that is problematic.
However many people find that just resetting (cancelling) the CE/DTCL is all that is required since the conditions that caused the CEL to illuminate were unusual and unlikely to be repeated. They conclude that the CEL illumination was spurious and in error. This is not normally the case,.
A good example is a misfire. As the driver you may be totally unaware of this condition were it not for the CEL. The system is far more sensitive than the driver.
The CEL may illuminate after a particularly heavy and unusual (for you) acceleration. The engine misfired under this TRANSIENT condition and set the CEL/ codes. However after resetting the CEL you may find that unless you repeat the severe acceleration that everything seems to have returned to normal. This is why the computer saves the conditions prevailing when the CEL was set.
The computer senses every single misfire (its that sensitive) but does not set the CEL until a pattern or a set number of misfires (individual firing stroke) has been reached. An occasional random misfire is to be expected and for this reason the computer filters out such activity below a set threshold value.
Hope this makes sense and clarifies the situation for you.
Get the codes read, recorded, reset the CEL and come back with the findings.
Don't go throwing money at the vehicle with a tune up, new plugs and filters etc unless these are overdue for change anyway UNTIL you have determined what codes have been set and whether the CEL returns.
Stuart
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