Check Engine Light On: How to Diagnose (OBD-II)

OBD-II device: your solution for what ails your car.

All cars built since 1996 are equipped with an industry-standard on-board diagnostic system. That system is always at work in the background, but will immediately alert you to a potential problem by turning on the check engine light and keeping it on until your car is serviced. There is no need to panic: as long as the light is stable and not flashing, you can perform a diagnosis yourself.

Get a Diagnostic Device

OBD-IIPurchase a diagnostic device. The current diagnostic system, also known as OBD-II, provides easy readout information to help you determine what is wrong with your car. Handheld diagnostic devices cost about $80 — what you would pay a mechanic for a diagnosis — and are available through your auto parts store. Choose one that is not specific to a vehicle brand, a device that can read and interpret data from any modern vehicle. See: What Does the Check-Engine Light Mean?

Locate Your Car’s OBD-II Port

That port is usually located under the lower dashboard on the driver’s side. Your owner’s manual will also list its location.

Connect to the OBD-II Port

Attach the cable portion (male) of the reader to the OBD-II (female) port. Press the on button to activate the reader and to obtain a read out. See: CNET: A Brief Intro to OBD-II technology

Interpret the Code

The screen of the reader will list a code, typically a letter followed by four numbers. For example, P0549. Certain code readers explain what the problem is by listing that information along with the code. Other readers provide a list of codes in a book that is included with the code reader. If the code is not listed in the book, it might be specific to your make only. Contact your vehicle’s service department for a diagnosis.

Reset the System

If the code suggests a problem that you can handle yourself such as a loose sensor, you can make the repair and attempt to clear the code from the OBD-II system. Your code reader may also come equipped with a reset button that will clear the code. If no reset button is available you can remove and reinstall the battery terminal in the reader. Then, restart your car and observe whether the code has cleared. If it has, then you have avoided a shop visit. If it hasn’t cleared, then contact your mechanic.

An OBD-II reader can pay for itself after just one use. You may prefer to see your mechanic anyway with the information obtained at least alerting you to the repair that must be made. Never ignore a check engine on light as whatever problem you have can worsen and cost you more money in repairs.


See AlsoProduct Review: Lemur BlueDriver OBD2 Sensor


Wikimedia file photo credit — Ahsanriaz6157  Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)


Author: admin
Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

1 thought on “Check Engine Light On: How to Diagnose (OBD-II)

Leave a Reply