Engine Management Light or EML Explained
Since about 1996 vehicles in most countries have been standardised to incorporate an Engine Management Light symbol on their dashboard. This universal warning light is illuminated to alert drivers of any engine running faults or transmission faults that may be present, by the vehicles ECU (Electronic Control Unit) This yellow on black symbol is often known as the EML, but most drivers still refer to it as the Engine Management Light.
The EML was originally introduced back then as a means to improve vehicle emissions by alerting the driver all was not well and their vehicle required attention. We believe that in some USA States, Traffic Officers were equipped with OBD (On Board Diagnostic) Scan Tools which enabled them to connect to any vehicles they stopped if their Light was on.
By retrieving codes or DTC’s (Diagnostic Trouble Codes) they could see how long a vehicle had been driven with the light on, infringing on that state’s emissions sometimes resulted in drivers being fined.
In Europe OBD Scanners or Scan Tools are often referred to as EOBD, this simply means European on Board Diagnostics.
Some vehicle owners are only concerned the EML is on if the vehicle has a running fault or if it’s due its annual MOT test. In the UK and probably in some other countries which we are not aware of, the EML has to be off for the vehicle to pass its annual MOT test.
Many non or less important Engine Management Faults can result in the Engine Management Light coming on, but on most vehicles, this does not affect engine driveability at all. Some vehicle owners when told why their EML is on, often reply “Now I know the reason why the lights on, and it’s not an important one, I’ll carry one using the vehicle anyway”. Vehicle Owners that say this aren’t actually as smart as they think they are, and here’s why.
There is only one EML and if it’s on for whatever known or unknown fault, how will they know if a further fault occurs?
MOT Test Failure if the EML is on
In the UK a vehicle fails it’s MOT if the Engine Management Light stays on with the engine running. The EML must be on when the ignition is switched on but go out and not come on whilst the engine is on. Any different to this and a Car, Van or Light commercial vehicle will fail the VOSA MOT test.
Faults present without the EML on
It’s fair to say that most vehicle owners are of the belief that the Engine Management Light will always illuminate or EML will stay on for any EMS (Engine Management System) faults. This is often not the case, and some EMS fault codes can only be read using a Manufacturer or Vehicle Specific Scan Tool. It is very common for fault codes to be present in the ECU but the EML not to be on, vehicle Manufacturers are not obliged by law to switch on the EML for all faults, only some.
Some owners will buy themselves a low cost OBD Code Reader and Deleter, these can be quite good at showing any stored “P” Codes and live data too. These cheap Scan Tools will allow the Engine Management Light to be turned off but there is a hidden danger you may be switching off the EML and preventing a garage from diagnosing the vehicle fully.
Warning before deleting the EML
Your vehicle may have Maker specific codes stored in the ECU that you cannot read with your OBD Scanner along with stored OBD codes you can read. What most people don’t know, and this will include quite a few Garages, is this.
DELETING THE ENGINE MANAGEMENT LIGHT WITH AN OBD CODE DELETER WILL OFTEN DELETE ALL MANUFACTURER SPECIFIC CODES YOU MAY NOT KNOW ABOUT. ERASING THESE WILL NOT HELP THE NEXT PROFESSIONAL GARAGE TO CARRY OUT THEIR USUAL DIAGNOSTIC TESTS BASED ON THE RETRIEVAL OF IMPORTANT STORED EML FAULT CODES.
As a general guide, if a fault code relates to an engines poor efficiency or anything that may have a negative impact on tailpipe emissions then the Engine Management Light will probably come on. If the EML is flashing, this normally indicates a misfire is present. EOBD or OBD fault codes will most often start with the “P” prefix meaning Powertrain, this covers both the Engine and Transmission.
OBD X BOX – What it can do
The OBD X BOX is a very advanced OBD Code Reader and Deleter with many unique features not found in any other Scanner or Scan Tool. When it comes to deleting the EML or switching off the Engine Management Light, it is probably the only EOBD Selected Code Deleter available anywhere.
The OBD X BOX is the only Scanner that can cancel the EML with the fault still present by deleting fault codes at up to 10 times per sec. this is very useful for turning off Limp Mode.