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Tips on How to Turn off Malfunction Indicator Lamp, Check Engine Light, and Service Engine Soon


Here are tips and details you should read to learn how to reset the check engine light in detail in case you have an emissions test to pass when your service engine soon or your check engine light is on.

Using a scan tool or by disconnecting the battery of your SUV, car, van, or truck, this article will give you an idea will help you understand that turning the check engine or service engine soon light off also means deleting all the emissions data from the vehicle’s (ECM) Engine Control Module.

You may turn off the check engine light using a scan tool or by disconnecting your car’s, truck’s, van’s or SUV’s battery. The smog machine won’t determine history or current emissions faults, erasing all Emission Monitors. It will be impossible for 1996 to a newer vehicle to pass a smog check without “completed” emission monitors.


We will describe the procedure to reset or how to turn the light off for you to get a better take on the OBD II Emission testing process.

With the Use of Trouble Code Scan Tool

OBD II Trouble Code Scan Tool is the safest and simplest way to turn the check engine light off. You can purchase a scan tool at any auto parts store in your area and use them not only to turn the check engine light off but also when you want to retrieve trouble codes stored or clear them. You can also read engine data live stream on some models. This method can be applied to 1996 and newer vehicle models only.

It is highly recommended that after retrieving stored trouble codes and scanning your OBD-II computer, you better take a better look at the trouble codes before deleting them. Keep a record of freeze frame data stored by ECU while setting them and the detailed code/s record for future purposes. This will be used when your vehicle needs a repair.

Freeze Frame Data

The recorded data of the ECU when it detected a problem in the emissions system. It’s the measurement of the actuator and sensor in frequency and/or voltage form. It triggers the MIL or check engine light on. Note that not all scan tools are able to display the freeze frame data even if the vehicle has collected and stored the data.

With the Use of The Battery Disconnect Method

While some of the late models won’t clear trouble codes using the method of disconnecting the battery, this might work on most vehicles available. The ECM ROM stores the trouble codes of vehicles which only a scan tool can turn off the (MIL) Malfunction Indicator Lamp, check engine or clear trouble code.

How to Turn Off The Check Engine Light

If you’re not using a scan tool, you must first locate the battery and proceed to disconnect the 12v negative cable from the terminal of the battery. This is the black wire which you’ll leave disconnected for 5 minutes. You must cycle the ignition to ON position 3 times while your battery is disconnected.

If you have the scan tool, you can try turning off the check engine light and follow directions from the manufacturer. Here, you need to find the OBD II DLC or Data Link Connector and connect it with your scan tool. Then, you can follow the scan tool manual.

Now you’ve deleted the data for readiness that took days, even weeks, to compile. You’ve also erased data that are related to important emissions which have no value to a smog technician repairing your vehicle.

The second step would start on making sure that you’ve turned off your ignition switch before trying to reconnect the battery. Reconnect the black wire or 12v negative cable to the battery terminal.

Next, switch your cycle ignition to on position and wait for a minute before starting your vehicle. Service Engine Soon Light and Check Engine Light should be turned off and reset.

Succeeding in turning off the check engine light means that the emission data was not stored by your vehicle in the computer’s ROM section and data on your engine’s vehicle such as radio & system settings and emission systems have been deleted.

The next step will be driving your vehicle under normal conditions for one week. This is the period when the emissions computer is learning back your vehicle’s emission components, systems, and gathering data. This is commonly referred to as the Drive Cycle. On-board Diagnostics or OBD II  emissions computer system should at least complete one cycle drive.

The emissions computer runs a sequence of internal tests during a drive cycle while the vehicle is being driven. This is to ensure that the emissions systems are all functioning properly. As computer completes its cycles, the Proper “readiness flags” are set and these test cycles are unique which is why they may require extended driving time to trigger on and run on very strict parameters. The data may widely vary of which the information on readiness flag and cycle data will be available on the service department of your dealership.

As soon as your engine starts when you drive, the vehicle turns on the Service Engine Soon light or the Check Engine as soon as an emissions fault is realized. The readiness flag will be refused to set by the emissions computer which means the check engine light would be off. Thus, failing the emissions test. You will only know this on a smog test on your vehicle. You’ll forfeit your inspection fee if the test center does not offer a free re-test.

You should take the smog test. Note that your vehicle may not be ready for the said inspection and that the emissions computer has not set the required parameters. You’d only find out if your vehicle is ready for the emission test after completing the smog test. The emissions computer tests may not be triggered by your normal pattern of driving, thus, failing to set required readiness flags.

Which method would you use?

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