How to Read Codes From Your Check Engine Light (For Older Cars)

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Introduction: How to Read Codes From Your Check Engine Light (For Older Cars)

About: I've worked for Instructables off and on since 2006 building and documenting just about everything I enjoy doing. I am now the Creative Programs founder and manager for Autodesk and just finished building o...
You can pay a mechanic a bunch of money to read your car's error codes when your check engine light comes on, or you can grab a paper clip and read the codes yourself.

After 1996 all cars were made to hook up to an external error code reader. Before 1996 however, cars reported their errors from the computer themselves via a flashing code from the check engine light.

The dreaded check engine light comes on while you are driving only to signify that there is a problem. The specific error or failing part could be one of many different things that the computer senses for. You can bridge a set of wires in your car and send the cars computer into its error reporting mode so that you can find out whats wrong with your car.

Again, this instructable is only useful for people who have cars that report engine trouble via a flashing check engine light. This should be true for many cars made before 1996.

Here is a short video explaining the code deciphering process. For the full instructions check out the following steps.


Step 1: Find Your Vehicle's Diagnostic Plug

The first step is to find your vehicles diagnostic plug. The one in my car was a small blue plug that was bundled together with another factory plug beneath my glove box on the passenger's side of the car.

Just stick your head up under the dashboard on the passenger side and look around for a plug that isn't connected to anything.

If you don't have a Honda Accord then do a search online for where your plug is located and you will probably find some good leads.

Pull the diagnostic plug out from the plastic housing that is bundling it to the other set of wires under there (I think the second set of wires down there are sensors for the ABS brakes or the airbags).

Step 2: Bridge the Wires

Get a paper clip or a piece of wire with the ends stripped off. Stick one end of the wire or paper clip in one of the holes in the plug and stick the other end in the other. Make sure that it's making contact with the wires buy pushing it pretty far down into the holes.

Step 3: Watch the Flashing Light and Decipher the Code

With the wire in place, put the key in the ignition and put the car into the "run" position. That's two clicks for Honda users.

Wait a second and keep your eye on the check engine light. You should see it start to light up in a series of flashes.

The light is blinking in a simple code of long and short. Long blinks mean "10" and short blinks mean "1".

My light was blinking once for a long time, and then twice for a short time. 10, 1 and 1 is error code 12. Code 12 indicates a problem with my EGR system. This is the system that sends some of the engine's exhaust into the cylinder to cool the combustion process and keep temps in the cylinders down. Having a broken EGR is relatively common on a high mileage car (I have 180,000 miles on mine) and it's a pretty easy fix. I was worried that I might have to pull over to the side of the road when I saw the light or get it to a mechanic ASAP, but now I know that it's not life threatening to the car and that it's OK if I get it looked at the next time I am at my mechanic.

You can find a list of error codes for the make and model of your car online by doing a simple search. The ones for Honda are included below.

Honda Check Engine Light Error Codes

0 ECU
1 Oxygen Sensor
3 Map Sensor
5 Map Sensor
6 Crank Angle
7 Throttle Angle
8 TDC Position
9 No. 1 Cylinder Position
10 Intake Air Temperature
12 Exhaust Gas Reiculation (EGR) System
13 Atmospheric Pressure
14 Electronic Air Control
15 Ignition Output Signal
16 Fuel Injector
17 Vehicle Speed Sensor
20 Electronic Load Detector
22 Vtec System Malfunction
23 Knock Sensor
41 o2 Sensor
43 Fuel Supply System
45 System Too Rich or Too Lean
48 Primary Heated o2 Sensor
54 Crankshaft Speed Fluctuation Sensor
61 Primary o2 Sensor Circuit
63 Secondary o2 Sensor Circuit
67 Catalyst Sytem
70 Automatic Transaxle
71-74 Random Misfire
80 Exhaust Gas Recirculation
86 Engine Coolant Temperature Circuit
90 Evaporative Emission Control System Leak Detected
91 Fuel Tank Pressure Circuit
92 Evaporative Emission Control System Insufficient

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My engine light came on while I was driving in my 1990 Honda Accord LX, so I pulled over and I listened to see if I could hear a new odd noise, I didn't. So I turned offrom my car then I started it back up and the engine light is now off. I found this site on how to scan the car. I did and my engine light just stayed on while I had the Bobby pin in, no flashes. What does this mean? My engine light hasn't come on ever sinceand that was a few days ago.

35 Comments

Was struggling with (the un-installation for short wiring and the re-installation of) this blue diagnostic clip until I've found this article (couldn't really crawled under to do it given the limtation in space, my car was parked along the through street's curbside). At least I get a clue about what's going on with the car prior to taking it to Autozone for free scan and some shops for price quotes. Thank you so much :)

Was struggling with (the un-installation for short wiring and the re-installation of) this blue diagnostic clip until I've found this article (couldn't really crawled under to do it given the limtation in space, my car was parked along the through street's curbside). At least I get a clue about what's going on with the car prior to taking it to Autozone for free scan and some shops for price quotes. Thank you so much :)

Nice article! It is a pain if the check engine light comes and you are short on cash or a code reader! If you are near one of the major chains they can usually provide you with a printout of what the OBD reading says on your vehicle. It might not work for older vehicles but people who own newer models (mid 1980s and later) should visit this site: http://www.checkenginefree.com At this site you will be able to see auto parts stores near to you that offer free check engine light readings! Check it out!

Good article! Check out this site I found that shows locations nearest to you that offer free check engine light diagnostics:

http://www.checkenginefree.com

Hope the site can help some folks out!

I have a 2003 kia Sedona with bad cat on bank 2 its a v6 front wheel drive so is it the front or back

I have a 1986 Honda Accord lxi, The pgm-fi light is coming on periodically. I checked the code from under the driver seat, and it is a #17. The Vehicle speed sensor. My problem is finding out where on the car that part is located. It still runs fine most of the time. I just want to replace it because I have to smog the car soon. And this way I'll get out in front of the problem.

I have a 1986 Honda Accord lxi, The pgm-fi light is coming on periodically. I checked the code from under the driver seat, and it is a #17. The Vehicle speed sensor. My problem is finding out where on the car that part is located. It still runs fine most of the time. I just want to replace it because I have to smog the car soon. And this way I'll get out in front of the problem.

I used the paper clip trick myself. I was skeptical at first, however I got a good solid read. My issue is... The code I am getting is not in my book. 4 short pause 4 quick. I have a 93 Honda accord with 370k mi. I think I have a burnt valve (amongst so many other things.) So perhaps is it reading manifold pressure? Anyone with any suggestions? So thank you for the paper clip trick!! I couldn't get a jumper wire from the guys down at autozone! They said that they dont carry nor does anyone make jumper wires for vehiles older than 1996. One of the guys there told me something simular to do, however, it did not work. Your explanation as well as the idiot proof diagram and video makes it impossible to not get it right! THANKYOU!!!

I've been wondering how to do this and shakii take it to autozone if it has the obd2

hy how can i read the codes of all new cars can u plz tell me

Auto Zone can ONLY do '96 and newer. I have a '92 Buick LaSabre and can not find anyone with a machine to diagnose the problem

Just as a heads up... Cleaning the EGR may resolve your problem if it's just clogged ;) As opposed to replacing it outright. If I recall correctly, GM computers will give a code 11 or 12 (according to their code system - I'm not exactly sure which one :p) before giving diagnostic codes. That would be the "Yeah, I'm working" code. Not knowing that and trying to read codes makes a good head scratcher puzzle while you figure that out :p

8 replies

Yes, code 12 on a GM vehicle verifies that the check engine light/computer diagnostic system is working properly. It will flash code 12 three times, then it will begin flashing each trouble code, three times starting with the lowest trouble code first, and continuing with each trouble code in memory, increasing numerically. When all trouble codes in memory have flashed three times, it will start over, (so that you know you're done reading codes) with code 12 again, and you can then remove the jumper. Oh, I guess I should have started out telling you that in order to pull codes on a GM vehicle, (with the exception of Cadillac) prior to 1996 you can use the same technique described in this instructable, but you'll be jumping A to B on the ALDL, (assembly-line diagnostic link). That plug is located near the driver's knees, on either side of the steering column, usually just underneath the lower edge of the dash panel. It will be a black plug, with 12 square holes in it, not all of the holes will have an electrical connector in them, but the A-B holes will always have connector visible in them. One more thing, don't forget to remove the paperclip, or jumper wire, because you'll be driving in diagnostic mode, which doesn't allow the vehicle to enter closed loop operation. Chrysler vehicles prior to 1996 are the easiest of all vehicles to pull diagnostic codes from. All you have to do on a Chrysler vehicle prior to 1996 is turn the ignition switch on, off, on, off, on, off, on and look at the check engine light which will be flashing trouble codes starting with the lowest one first and increasing to the largest one last. If anyone is interested in learning how to pull trouble codes from a Ford vehicle prior to 1996 let me know, and I'll write an Instructable for that. It's a little more complicated, and that is the only time you use an analog meter on a computer-controlled vehicle!!! Any testing on any computer-controlled vehicle which requires a meter has to be done with a HIGH IMPEDANCES DIGITAL MULTIMETER ONLY!!! The coil in an analog meter can, and will blow a number of circuits inside automotive computers. I hope this helps everyone, and have a great day.

"If anyone is interested in learning how to pull trouble codes from a Ford vehicle prior to 1996 let me know, and I'll write an Instructable for that. It's a little more complicated, and that is the only time you use an analog meter on a computer-controlled vehicle!!! Any testing on any computer-controlled vehicle which requires a meter has to be done with a HIGH IMPEDANCES DIGITAL MULTIMETER ONLY!!! The coil in an analog meter can, and will blow a number of circuits inside automotive computers. I hope this helps everyone, and have a great day." I am interested in the Ford procedure 1985 E-150 6cyl

Folks I'm sorry for digging up an old instructable, but I'm getting nothing when I jumper pin A to pin B. It's a 1988 chevy van G30 with 5.7 L TBI engine. I had fuel pouring out of the TBI area and so I replaced the top part with a rebuilt one, but now it's not starting. Should I conclude that the ECM is bad because I'm not getting anything in the dash when I jumper the 2 pins? Wires from ECM to injectors checked out ok. Thanks in advance

Im interested in any information you have I have a 94 mustang 5.0 ho automatic it runs great but once in awhile turn it off and wont start turns over fine fuel presure none but when fuel presure is good still wont start untile you unhook the battery and it resets itself then runs great again untile next time . thnx email is froggiestyler@hotmail.com

hey i have a mustang 1994 and the check engine light came on, i replaced the egr sensor. nd the valve.. the light went off for a few hours then it came back on, the next day it turned off in the morning.. then a few hours i was in the freeway and my car started to slow down i kept pressin the gas pedal and it did not go so i pulled to the side turned it off and tried turnin it back on and did not start .. the light came baack on and i tried usin the paper clip thing but it dont work,, any help??

hi, my name is George, I'm trying to get the codes from y dads 1990 tempo, wenjt to autozone and they told me the car is to old for them to pull the code, any help would help, thanks. my email is scura9@aol.com

Hello  Im very interested in knowing how to read codes on a 1992 Ford Ranger 4 cyc  thanks

I have a 1994 Lincoln towncar how to i get the trouble codes engine idles rough and stalls at red lights