Read Your Car's Trouble Codes and Fix the Problem Yourself
Your cars check engine light is designed to let you know there is a problem with
one of your car's computer monitored systems. This will be a sensor or a mechanical
failure of some kind. The check engine warning light is also known as a service
engine soon light or a MIL (malfunction indicator light). Fortunately though your
car's computer system is programmed to identify the problem by producing a trouble
code which will point you in the direction of the problem and determine if the
car is safe to drive or not.
By using a simple code reader such as an Actron CP9185 which is available from
Amazon starting at $35.00 (US) anyone can gather these codes and fix the problem
themselves. This scanner will read engine, transmission and emission codes. If you
want to read airbag safety, traction control and ABS codes you must upgrade the
scanner to the more expensive model such as the CP9680 for about $300.00.
There are two types of reader tools which define different levels of information
which is: Retrieving the troubles codes, and reading the live data stream of each
sensor which is typically reserved for mechanics.
Don't let this scare you though because nine times out of ten the problem is
a simple sensor, spark plug, ignition coil or injector replacement. In this guide
we will show you how to gather codes and show you the most
reasons the check engine light will come on, but first how to read the codes.
No matter which tool you choose or the codes you want to read they all will be
accessed through the ALDL "D" shaped 16 pin connector located under your car's dashboard
on the driver’s side in plain sight in most cases. This serial connector is used
to transfer the code data from the vehicle’s computer to the code reader or scanner
so it can be easily displayed and read. If you cannot find your car's connector
it should be mentioned in your owner's manual. Sometimes the connector can be behind
a small plastic trap door. This is mostly in Mercedes Benz and BMW cars.
Let's Get Started!
Begin with the vehicle's engine off with the transmission in park.
Connect the Code Reader: Open the driver's door and locate the ALDL
connector. Then securely insert code reader plug onto the connector. Be sure the
connector is in good working order and that the plug stays securely in place.
Activate the Code Reader Tool: Insert the ignition key and turn it to
the on position. The dash warning lights will come on and the gauges will start
to work, do not crank or start the engine. If you accidently start the engine simply
turn the engine and ignition switch off and disconnect the scanner, then re-plug
it in again to restart the procedure. Some cars have a two-step ignition system.
The first step will not illuminate the warning lights and the tool will not work.
You want to have the dash warning lights on to start the reading process.
The code reader will then power up and display the welcome screen. If the screen
does not come on wiggle the reader connector while in ALDL data port. Sometimes
the pins can become a little corroded because of moisture which will make the connection
questionable. Wiggling the connector will help break through this rust and create
a proper connection. If the reader still doesn't power up retry the reader on an
alternative car to make sure it is working.
Read the Codes: After the welcome screen appears follow the prompt which
will include: Read Codes, Clear Codes, MIL Status, I/M Data, Freeze Frame Data and
Code Review. While using the up and down arrows select the "Read Codes" option.
This will allow the reader to configure a connection to the automobiles computer
and accept the error code or codes to be displayed on the reader.
This will initiate the code reader's gathering code sequence while it communicates
with the cars computer which can take up to 20 seconds to complete. The computer
will then deliver all trouble codes stored in its error memory and transfer them
into the code reader for display. If the reader or scanner "hangs" on the "working"
screen for over two minutes turn the ignition key off and unplug the reader from
the ALDL connector. Wait a few seconds and then plug it back in to the ALDL port
and turn the ignition switch back on to restart the process. What sometime happens
is the data gets "stuck" and the operation needs to be rebooted much like a normal
home or work desktop computer.
Within a few seconds the reader will display the trouble code or codes. If there
are multiple codes stored it will say 1 of 2 or 1 of 3 which is an indication of
more than one code is present. This will be displayed at the top of the screen on
the right hand side. Use the up and down arrow buttons to toggle between the codes
so you can identify each code and start the repair or have an idea of what the problem
is when you take your vehicle into the repair shop.
On the main display screen will be the code along with the definition of what
the code is which denotes the system or sensor that has malfunctioned. In this case
a PO336 code is telling you that the crankshaft angle sensor has failed or has failed
intermittently which causes the engine to stall or not start entirely. Here is a
chart of OBD2 trouble code
definitions. Occasionally you will have problems gathering the codes and the
code reader will display a
which means the code gathering was incomplete.
If you feel the code was set by error such as a sensor was disconnected during
a repair or service while the ignition key was turned on or if a repair has been
made you want to erase the code follow the prompt to
the trouble codes.
Remove the Code Reader: To remove the code reader from the car, simply
turn the ignition key to the off position. The instrument cluster warning lights
should be off.
Grasp the connector firmly and pull gently outward to unplug the code reader
connector and separate it from the ALDL data port. Replace the cover over the port
if equipped to prevent any corrosion causing moisture that could cause damage to
the connector. Once the code reader or scanner is disconnected find a cool dry place
to store it in such as the top drawer of your tool box, that's where most mechanics