How to Use OBD Systems to Diagnose Your Car Problems

In the late 1980s and early 1990s, auto manufacturers began including self-diagnostic systems in new cars.  Not all automakers began installing these diagnostic systems at the same time.  When they were first implemented, the different manufacturers' systems were very different from one another.  Eventually, the system's became standardized and became known as On-Board Diagnostics (OBD). 

Modern diagnostic systems will report problems to you through the use of an OBDII scanner.  You will usually notice you have a problem when the Check Engine light or MIL (Malfunction Indicator Lamp) remains lit in the driver's console while driving.  This serves as a visual indicator to the driver that there is a malfunction or possible problem with the vehicle and it needs attention.  When a scan tool is connected to the vehicle, it can report the various error codes for the problems that the vehicle has detected.  Most codes are standard across vehicle manufacturers, but each manufacturer may also have an additional set of manufacturer specific codes available.

OBDI and OBDII Systems

OBD1 was the first standardized automobile self-diagnostic system - this system is usually found on vehicles from the early 1990s up until about 1995.  In 1995 OBD2 was mandated as the standard for all US automobiles. Other variations of the diagnostic systems exist, however, OBD1 and OBD2 are the most commonly known.

If you have a car that has an OBD2 system, also known as OBDII, you will need a port scanner to read the codes for your car.  If you do not have one, auto parts stores will generally read the codes for you for free.  You can also choose to buy your own scanner such as this Equus 3100 Innova CanOBD2 Diagnostic Tool  (I have not tried this particular scanner, read the reviews on Amazon).

I have the BAFX Products scan tool for Android Devices, which connects to my phone through a Bluetooth connection and it can read the codes from my vehicle.  There are several free and paid apps available that will work with this scan tool.

OBD1 cars can be read by port scanners as well, however, some of them such as the 1993 honda accords did not require a port scanner, they were read by jumping a connector and reading the output by counting flashes on the various lights in the driver's console. Other vehicles were read by led readouts.

Scanning your vehicle for OBD Diagnostic Failure Codes

The first thing you need to do is locate your port and if required, a port scanner.  On the 1993 Honda Accord, the diagnostic port is located behind the passenger side kick panel. On later models such as the 1998 Honda Accord, the connector is located on the driver side of the vehicle under the dash.

Next, either connect your port scanner or in the case of the 93 Accord, jump the connector with a paperclip.  Turn the ignition to the on position.  If you are using a scanner, the OBD codes will appear on the readout, if you are jumping the diagnostic port leads, the codes will be output via the check engine light.

Once you have the codes, you may research their meaning online or in your automobile repair manual. I have used the Haynes 1990-1993 Honda Accord Repair Manual and have found it to be pretty useful.  They also offer a book on OBD-II and Engine Management Systems which I have not used - read the reviews on Amazon for details on it.

This blog post shows in depth how to read the OBD1 diagnostic codes on a 1993 Honda Accord.