How to Read Codes Without a Scan Tool on a 1994 GM

by Blaze Johnson
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Checking trouble codes from your 1994 GM vehicle does not require the use of special equipment, such as a scan tool. Extracting trouble codes from your vehicle lets you track down and diagnose faulty components in an expedited manner. The computer uses the "Check Engine" light located on your dashboard to display the stored trouble codes. When placing the computer in diagnostic mode, the "Check Engine" light will flash in numbered sequences that represent specific trouble codes.

Step 1

Turn off your GM's engine. Locate the black rectangular shaped diagnostic connector, which underneath the driver's side dashboard panel near the floorboard.

Step 2

Bend a small metal paperclip into a "U" shape. Insert the pointed ends into the furthest two top-right diagnostic connector terminals. After bridging the two top right terminal connections on the diagnostic connector, switch the ignition to the "ON" position.

Step 3

Watch the "Check Engine" light on your dashboard. It should flash once, pause, and flash two more times in succession. The "one flash followed by two flash" code will occur a total of three times before the computer displays the trouble codes stored in the computer's memory.

Step 4

Write down the sequence of flashes displayed from the "Check Engine" light after the initial "one flash, pause, two-flash" code appears three times. The remaining trouble codes will flash a total of three times before displaying the next set of trouble codes. After the computer displays all of the trouble codes, the "Check Engine" light will repeat the sequence, starting with the "one flash, pause, two-flash" code.

Step 5

Turn off the ignition switch. Remove the paper clip from the diagnostic connector. Translate the number of flashes for each sequence into the appropriate two-digit GM trouble code. For example; if one flash sequence flashes three times, pauses and then flashes four times, the sequence would be considered trouble code "34."

Step 6

Research each of the trouble codes you wrote down to find out information regarding the components affected (see Resources).

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