Service Engine Light Reset Procedure
On some automobiles it’s called the check engine light. On others the warning says service engine. Regardless of what the icon says this light comes on when there is a malfunction in the computer controlled emissions system. AutoRepair.Answers has an in depth article covering why the light comes on.
Also covered is the most common check engine light causes along with strategies for diagnosis and problem solving. This article will focus on performing the service engine light reset procedure without a scan tool and the side effects associated with disconnecting the battery and draining the stay alive memory.
Service Engine Light Reset
When this light comes on drivers would like to turn it off. It’s bright, colorful and can be a distraction during night time driving. From a professional mechanic’s point of view the warning light is associated with an important message from the vehicle’s on board computer that can be valuable in diagnosis. For this reason it is highly recommended to purchase an inexpensive scan tool that can erase and read the codes. Write the numbers down before hitting the clear button in case they are needed for future diagnosis.
Wanting to reset the warning light is a valid wish that has some beneficial diagnostic implications. When repair shops are following diagnostic tree charts for set codes, often the first step in the ladder diagram is to clear it, then drive the car to see if it returns. This procedure identifies the problem as intermittent or a hard failure. In the case of a hard failure the light will come back on immediately or within a few drive cycles. With an intermittent situation the code may not reset for weeks, months or years.
How to Clear Codes without a Scanner
On automobiles older than 1996 disconnecting the battery for a few minutes will take care of clearing any set trouble codes. On vehicles newer than 1996 with OBD II (on board diagnostics second-generation) the procedure is a little more complicated. These cars and trucks have a stay alive memory. In this situation voltage or electrical energy is stored in a capacitor. This capacitor is capable of holding memory settings for hours or even days depending on the year make and model.
Included in the memory settings are the diagnostic trouble codes responsible for triggering the illumination of the amber warning light. In order to perform the reset procedures without a scan tool it will be necessary to drain the power from this capacitor. With the battery disconnected you can turn on the hazard warning lights and operate the horn. These two systems are powered regardless of the ignition key position, also referred to as hot at all times. This allows these accessories to drain the power stored in the capacitor responsible for holding the memory.
Side Effects of Clearing Stay Alive Memory
The negative side effects will vary greatly depending on the year of the vehicle and the manufacturer that built it. Some car companies only have a few basic settings stored in long-term memory. Here are a few of the things you might find after reconnecting the battery and driving the automobile. The engine will probably experience erratic idle for several drive cycles because the computer had a learned idle setting. This is where it compensated for dirt and carbon build up in the throttle body by adjusting the IAC (idle air control) motor.
Another setting that was collected and now lost is transmission shift point information. As people drive the on board computer learns the habits of the primary driver and adjusts the shift patterns to provide the best fuel economy and feel on the road. Since that information has been wiped out it will take several drive cycles for it to relearn normal patterns. This can cause harsh and early shifts for several days.
Automotive scan tools have really come down in price thanks to the power of competition. The most basic of these handheld devices are considered code readers because they can only read and erase. Although they cannot access the data stream for intense diagnosis they are capable of re-setting the service engine soon light without any of the negative side effects that come along with disconnecting the battery and draining the stay alive memory. With entry-level tools costing around $20 it’s hard to find a good reason to use any other method.