How to Turn Off The Check Engine Light, Service Engine Soon or MIL?
If you're performing this procedure in an effort to pass an emissions test when the check engine light or service engine soon light is on or illuminated, read on and in detail to learn how the check engine light reset procedure works.
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.
You may have already read information describing how to turn off the check engine light or service engine soon light prior to the emissions test in order to pass the smog inspection. We'd like consumers to understand that by turning off the check engine or service engine soon light, essentially deleting all emissions data from your vehicle's engine control module (ECM), the smog machine will not know your vehicle has had or currently has any emissions faults AND all Emission Monitors will be erased as well. Without "completed" emission monitors a 1996 and newer vehicle has no chance of passing the smog check.
We will describe the reset or "turn light off" procedure so you may understand the OBDII emissions testing process and how the check engine light or service engine soon light apply to the emissions test.
Using a Trouble Code Scan Tool
The simplest and safest way to turn off the check engine light is by using an OBD II Trouble Code Scan Tool. You may buy a scan tool at your local auto parts store. It can be used
to retrieve stored trouble code(s), clear trouble code(s) and turn off the check engine light, read live streaming engine data (on some models). The OBDII Scan Tool method of turning off your vehicle's check engine light only applies to 1996 & newer model vehicles.
Battery Disconnect Method
The battery disconnect method will work on most vehicles. Some late model vehicles will not clear trouble codes by disconnecting the battery. On these vehicles trouble codes are stored in the ECM's ROM, and only a scan tool will clear trouble code(s) and turn off the check engine or malfunction indicator lamp (MIL). Perform the battery disconnect method at your own risk!
Instructions on How to Turn Off The Check Engine Light:
Step 1. If not using a scan tool, locate your vehicle's battery. Disconnect the 12v positive cable (red wire) from battery terminal (+). Leave it disconnect for 5 minutes. While the battery is disconnected, cycle the ignition switch to ON position 3 times.
If using a scan tool to turn off the check engine light, follow manufacturers directions. You will need to find your vehicle's OBD II Data Link Connecter (DLC) and connect your scan tool to the DLC, then follow the steps indicated on your scan tool or scan tool manual.
- You've just erased important emissions related data which is invaluable to a smog technician attempting to repair your vehicle.
- You also deleted very important "readiness flag" data which takes days, if not weeks to compile.
Step 2. Insure ignition switch is OFF. Reconnect the battery 12v positive cable (red wire) to battery terminal (+).
- You're risking electronic component damage. High voltage spark produced during the reconnection of the positive 12v cable can cause damage to fragile electronic emissions component/s.
Step 3. Cycle ignition switch to ON position and wait 1 minute, then start your vehicle. Check Engine Light or Service Engine Soon Light should be reset and turned OFF.
- If you are successful in turning off the check engine light, this means your vehicle has not stored it's emissions data in the ROM section of it's computer and you have just deleted all data pertaining to your vehicle's engine and emissions systems, sometimes including security, radio & system settings.
Step 4. Drive your vehicle for one week under normal driving conditions. During this period the emissions computer is gathering data and re-learning your vehicle's emissions components and systems. The emissions computer OBDII (on-board diagnostics) system must complete at least one drive cycle (in some cases two or three).