Trouble Code Read

Step by step instructions on how to read automotive diagnostic trouble codes. This article pertains to most vehicles built after 1996.

Difficulty Scale: 2 of 10

Tools and Supplies Needed

  • Code Reader
Begin with the vehicle on level ground, in park, with the parking brake set.

Step 1
- When a check engine or service engine soon light illuminates the computer system has detected a malfunction which indicates a repair is needed.

Check Engine Light

Step 2 - Obtain a simple code reader which are available from about $25.00. These readers are available on Amazon.

Trouble Code Reader

Step 3 - Next, locate the ALDL data link connector which is usually under the dash on the drivers side, attach the reader data connector.

Reader Connector

Step 4 - With the data connector in place, turn the ignition key to the "ON" position. (Note: Do not start the engine.)

Ignition Key "ON"


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2015-01-06)