Learning how to retrieve obd trouble codes stored in the computer’s memory when the Check Engine light or Malfunction Indicator Light (MIL) illuminates on your car’s dashboard can make repairing your car less of a puzzle. These on-board diagnostic trouble codes point you in the direction of the potential problem. For example, a trouble code may reveal an abnormal change in behavior in one or more of your engine circuits or sensors, affecting part of the emission control system: A failed crankshaft position sensor (ckp), camshaft position (cmp) sensor, mass air flow (MAF) sensor, or any other sensor or its electrical circuit.
To diagnose complex electronic problems in newer cars, car technicians now need varied skills, special equipment, knowledge, and experience. Thus, if you lack proper training and equipment, sure you’ll have a hard time trying to solve every car emission problem just by pulling and interpreting diagnostic trouble codes.
On the other hand, not every single engine system problem is too difficult to deal with, specially if you get the help of your repair or service manual.
In this guide, you’ll find suggestions to help you deal with trouble codes that point to simple repair jobs that may come your way, and how to deal with the more difficult ones.
How to Retrieve OBD Trouble Codes
First Generation On-Board Diagnostic (OBD-I) Systems
Before the appearance of the on-board diagnostic generation two (OBD-II) system in 1996, car manufacturers used different methods to retrieve data from the computer’s memory and had their own code designations for each particular failure.
On Chrysler models, for example, you need to turn the key On and Off three times and then count the Check Engine light number of flashes to access diagnostic codes. To access the codes on a General Motors model, you may use a jumper wire or paper clip to bridge the designated terminals on a diagnostic connector, usually found under the dashboard, and take note of the number of flashes from the Check Engine light. Getting the trouble codes on a Ford model is quite similar, except you use an analog voltmeter and count the number of times the needle on the voltmeter deflects to get the code number. The diagnostic connector on these models is usually located in the engine compartment.
Even so, on OBD-I systems, you may be able to use an auto code reader to retrieve the codes. Most auto parts stores carry simple code readers and scanners, and you can also buy them online. Before buying one, though, if you own a pre-1996 car model, consult the repair manual for your particular vehicle make and model, or a computer codes manual, so that you know exactly how to retrieve the codes. Most auto parts stores carry these manuals as well.
Your vehicle repair manual or the computer codes manual will help you interpret the trouble codes. Just keep in mind that OBD-I codes may differ from one vheicle model to the next, so make sure to look up the code for your particular vehicle make and model.
Second Generation On-Board Diagnostic (OBD-II) Systems
Today, vehicles come equipped with complex engine control systems that require expensive equipment to access and analyze all or most of the data stored in a car’s computer during a failure. The good news is that the trouble codes you are most interested in on OBD-II systems have been standardized, so they have the same meaning across manufacturers” vehicle models. And you can buy relatively inexpensive aftermarket scan tools that let you retrieve some of the diagnostic codes you can use to troubleshoot simple engine control system problems and do maintenance work.
A scan tool, along with your repair manual, can help you save hundreds of dollars a year in simple repairs. And the more you learn about your car systems and how they work, you’ll gain experience to do more maintenance and other easy repairs on your own car.
On 1996 and newer vehicle models, you can use a code reader or scan tool to retrieve the codes. Connect the tool to the data link connector found underneath the dashboard, on the driver’s side. Then, follow the instructions that come with your tool, or your repair manual to retrieve the codes.
Your vehicle repair manual or the computer codes manual will help you interpret the trouble codes.
Why Your Computer Stores an OBD Code
Your car’s computer constantly receives information from sensors and sends information to actuators as electrical signals. The number of systems the computer “talks” to depends on your vehicle make and model.
To know that systems are working properly, the computer compares the received information with the data stored in memory. If one of the received signals doesn’t match a preconfigured value or range of values, the computer may store a trouble code and turn the engine light on or wait for another drive cycle to confirm a potential problem. This depends on the type of failure it detects. But once your car’s computer confirms a potential failure, it’ll save the specific trouble code(s) and alert you.
You then may retrieve the code(s). As described above, you may get the code through the data link connector using a piece of wire, a voltmeter; by turning the ignition key; through a code reader or scan tool. The best way to proceed is to follow the instructions in your vehicle repair manual for your particular make and model. If you can retrieve the codes using a code reader or scan tool, follow closely the instructions that come with your tool.