Auto Code Readers

Auto Repair Codes - Manual Code Reading

Using a Jumper Wire to Flash Codes

Most vehicles display thier Petrol and Diesel Engine, ABS Brakes, Airbag and Auto Transmission codes by flashing a light on the dashboard of the car.

One thing that you can use as a jumper wire is a "Steel Paper Clip" that has been straightened out as shown in the diagram to the right. It must be a steel one, and not have any plastic coating on it.

Using a paper clip or a piece of wire as a jumper wire is PERFECTLY SAFE. Using jumper wires to flash codes has been built in by the car manufacturers to ensure people without a Scan Tool or Code Reader can still diagnose the vehicle faults by reading the codes.

Paper Clips

Simply follow the step by step instructions which clearly show you which terminals on the diagnostic connector to link, and then insert the Paper Clip into those terminals.

The picture to the right show a typical example of bridging 2 terminals of a diagnostic connector to start a Check Light flashing on the dashbaord.

Jumped OBD2 Connector

The website pages will now generally ask you to turn the Ignition Key On.

A Check Light on the Dash will now begin to Flash as shown in the diagram to the right.

Flashing Check Engine Light

By using the code timing information, you can now understand the pattern of the light flashes, and you can write down the code numbers as they are flashed in sequence.

You can then enter the code numbers into the final Codes Screen to get the code description (code meaning).

Using an LED Tester or Voltmeter to read the codes

Some vehicles such as pre 1998 Mitsubishi's and Hyundai's, plus some Kia and Mazda vehicles do not display codes on a flashing dash light. These vehicles give thier code signals directly from the diagnostic connector. You will need to use an LED tester or a Voltmeter to read the codes from these vehicles.

If you don't have a voltmeter or an LED tester you can easily make an LED tester for under $1, as detailed in the steps below.

How to make an LED tester to read the codes for less than $1

Step 1
Solder a 10K ohm resistor on to the positive (longer leg) of an LED. You need the 10K ohm resistor to limit the current draw from the vehicles diagnostic lines. The LED will still be bright enough to see flashing.

Step 2
Solder one wire onto the bottom of the resistor. Solder another wire WHICH IS SLIGHTLY SHORTER THAN THE FIRST WIRE onto the remaining LED leg. The Longer wire is your Positive (+) wire. You should now have something looking similar to the picture below. This basic LED tester will work perfectly well, and allow you to read the codes with the Manual CodeReader Instructions.

Soldered LED

If you choose you can now heatshrink the two LED legs and add Aligator clips to make it easier to connect to some of the vehicle diagnostic connectors.

LED with Aligator Clips

To use the LED tester simply connect it to the vehicle as per this websites instructions. You may need to try the LED in both directions to get the correct polarity to make the LED flash. This WILL NOT cause any problems, as it simply won't draw ANY current in one direction (LED off), while in the other direction it will be ON or flashing.

By using this websites code timing information, you can now understand the pattern of the LED light flashes, and you can write down the code numbers as they are flashed in sequence.

You can then enter the code numbers into the Code Screen to get the code description (code meaning).

How to use a Multimeter to read codes

You can use any standard digital multimeter to read the codes. It can be a very low cost, simple meter. It only has to be able to measure 0 to 12 volts. You can use an Analog Voltmeter, however you need to make sure it has an internal resistance of at least 10K ohms to be safe. Multimeter
I find that if you have an Auto Ranging digital multimeter, that it is easier to set the voltage range manually (if possible) to a low range (say 10 volts) so that the screen goes between around zero volts up to OL. This also means if your meter has a bar graph on the bottom of the screen, it will move right across the screen and back making it easier to count the code output pulses. 0v Reading on Multimeter
Please note: A digital multimeter probably wont show exactly zero volts when connected to the car diagnostic terminals. This is OK, as you are simply looking for a major change in voltage. The car code output systems will swing between either approx. 0 and 5 volts, or approx 0 and 12 volts. OL reading on Multimeter


Other Things That Can Help You With Auto Repair and Manual Code Reading

Black Jumper wire loose terminals Yellow and Red jumper wires


The Black Jumper wire in combination with the loose terminals shown above is really useful for grounding terminals of vehicle diagnostic connectors, to output the codes. One of their main advantages is that they provide a stable ground, to ensure the vehicle stays in diagnostic mode to display the codes while you read them.

The 3 loose terminals above are also really useful for accessing some diagnostic connector terminals that are hard to get to. You can simply push the into / onto the diagnostic terminals and then hold or clip you LED tester or Voltmeter leads onto the terminals.

The Yellow and Red jumper wires above are designed as "generic" jumper wires to link terminals of the diagnostic connectors.


You use this information at your own risk. Always be sure to follow the instructions carefully. Rennacs is not responsible or liable for any mistakes or omissions in the information provided, or any mistakes made by anyone following any of this information.