Easy 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
Begin with the vehicle on level ground, in park, with the parking brake set.
- When a check engine or service engine
soon light illuminates the computer system has detected a malfunction which indicates
a repair is needed.
Step 2 - Obtain a simple code reader which are
available from about $25.00. These readers are available on
Check Engine Light
Step 3 - Next, locate the ALDL data link connector
which is usually under the dash on the drivers side, attach the reader data connector.
Trouble Code Reader
Step 4 - With the data connector in place, turn
the ignition key to the "ON" position. (Note: Do not start the engine.)
Step 5 - Once the ignition power has been turned
"ON", the code reader will power up and display the welcome screen.
Ignition Key "ON"
Step 6 - After the reader has powered up, follow the
prompt and select "read codes".
Reader Power On
Step 7 - Next, the reader will enter "gather codes"
mode which will retrieve any codes the computer has stored.
Select Read Codes
Step 8 - Within a few minutes the reader will display
trouble codes which denotes the system or sensor that has malfunctioned. In this
case PO336 is a crankshaft angle sensor failure.
Step 9 - Once the codes have been displayed the reader
will give an option of clearing the code which is done by pressing the "clear" button.
After pushing the button the reader will erase all codes present in the computer.
Retrieved Trouble Code
- The reader will present an option to
recheck the system and give a "PASS" reading if the system detects no problems.
Step 11 - After the reader has finished, turn the
ignition key to the "OFF" position.
Step 12 - Next, remove the data connector from
the ALDL port.
Turn Ignition Key Off
Once the "check engine" or a "service engine soon" light has illuminated the
computer has detected a problem and stored one or more trouble codes. When this
light is illuminated the vehicle enters into "limp mode", which means the system
is not running at optimal performance. Most 1996 and newer vehicles utilize an ALDL
connector port which is used to connect a reader for code retrieval. This connector
is generally located on the drivers side near the foot well.
A trouble code definition
Remove Data Connector
can be used to help define the meaning of the malfunction. After repairs
have been performed and codes cleared, the computer will start testing systems once
the vehicle is driven. These monitors operate during normal driving conditions and
can take up to 30 miles to complete. If the computer senses a problem, the check
engine or service engine light will re-illuminate.
Vehicles older than 1996 use an OBD1 scanner or the use of onboard retrieval
method is required to gather trouble codes
- If a scan has been performed and a
P1000 is observed it means
the computer could not complete the retrieval process.
- If the check engine or service engine soon light does not illuminate while
the key is in the "ON" position repairs are needed such as an indicator bulb
Article first published 2016-02-03