Is your check engine, MIL (malfunction indicator light) or service
engine soon light on? This light is designed to let you know there is a
problem with the engine management, fuel system, emission system, EVAP system or
transmission of your car. Every vehicle built after 1996 is equipped with a
computer that runs on a common base system called OBD2 (on board
diagnostics) which is more uniform and easier to use than its predecessor
Common base means
when the system has trouble, a failure of some kind, the system can identify
this problem by producing a trouble code which is commonly identified across all
manufactures by law. These codes are called P codes
and will always start with a P followed by a four digit number such as P0141
oxygen sensor replacement, or the P0300 code series,
misfire detected, P0301, P0302, P0303, and so on for each cylinder.
You can get a scanner from Amazon for about $90.00 bucks such as the Actron
CP9185 that will read engine and emission codes. If you want to read
transmission, airbag safety and ABS codes you must upgrade the scanner to the
more expensive model such as the CP9680 for about $300.00
Please watch the video below to learn how to check your codes and then
continue down the article to read tip and additional information.
Using a simple
scan tool you can plug into the 16 pin ALDL connector located under the dash
on the driver’s side (in most cases) of your vehicle. There are many different
kinds of scan tools from the OEM units which are expensive, constantly changing
and need updating and are difficult to use, or you can opt to use a cheaper easy
to use unit which is best in 97% of all check engine light cases.
9 times out of
10 a sensor has failed such as an oxygen sensor's heater has burned out, or
there is a leak of some kind such as an EVAP hose that has a tear or an O ring
seal is leaking. The beauty of computer systems is that they have made it
easier, not harder to fix vehicle problems since the introduction of the OBD2
Many engine misfire and running problems can be solved with a
Once the check engine light has come on and the repairs have been made the code
will need to be cleared, back before 1996 you could simply disconnect the
battery to clear the codes that is not the case with OBD2 systems. Once cleared
by a code reader or scanner the vehicle will need to be run through a series of
cycles before the computer monitors will keep the check engine light off.
other words the vehicle will need to be driven usually for a few days before the
computer system will deem all systems okay and keep the check engine light
off. When the ignition key is in the on position without the engine running
the check engine light should be on and then go off once the engine has been
started. If the check engine light does not come on with the ignition key in the
on position suspect a bad bulb or fuse.
If the check engine light is on while driving the computer system is
in "limp" mode and will run on a set of preset values to allow the engine to
keep running. It is important to note that while in this mode mileage and power
will be downgraded along with the vehicle not being able to pass smog at its
biannual smog inspection in California and other states that require an emission
Now let’s go over each step so you can see how easy it is to read your check
engine light codes: Begin with the vehicle on level ground, in park, with the
parking brake set and the engine off.
When the light is on this is confirmation that the computer has a code stored for retrieval which
will guide you to the needed repair. This light can turn on even when there is
no noticeable problem with the way the vehicle is running. This is because one
or more of the supporting systems such as emission system is having a problem
which does not affect the way the engine runs.
Obtain a simple code reader, which
are available from about $25.00. These readers are available on
Amazon. Every vehicle owner should have one in their tool box or glove box
compartment because the check engine light is the number 1 problem with today's
vehicles. Your vehicle will have many check engine light problems over its
lifetime, plus it is cool to check your friends or family member’s codes and
help them out as well.
Try not to get the cheapest reader because they can break
easily or not last very long whereas the middle of the road scanner can last
longer and be more durable, the top of the line reader is nice, but not
necessary. Besides you will need the extra cash to by the parts needed to fix
your vehicle. By the way
Amazon is the best place to purchase your vehicle replacement parts.
done my research and they beat their competitors’ prices while giving you a
higher quality part. They also can get it to you much faster with an awesome
return policy just in case the part you buy is not the problem, believe me this
Next, locate the ALDL 16 pin data
link connector which is usually under the dash on the driver’s side. Sometimes
the connector can be behind a small plastic trap door; this is mostly in
Mercedes Benz and BMW’s, in other vehicles it will be in plain sight. This
serial connector is used to transfer the code data from the vehicle’s computer
to the code reader or scanner then it can be read and easily displayed.
cases the ALDL connector can be located in the center console under a small
plastic cover. If you cannot find the connector it should be mentioned in your
owners or a repair manual.
With the driver’s door open and the code reader or scanner in hand and with
the ignition key in the off position,
take the plastic plug connector which is attached to the reader and securely
plug it into the ALDL connector. Be sure the connector is in good working order
and that the plug stays securely in place.
With the data connector in place,
turn the ignition key 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 off and disconnect the
scanner and 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,
you want to have the dash warning lights on to start the reading process.
Once the ignition key power has been
turned to the on position without the engine running. The code reader will
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
corroded because of moisture which makes the connection questionable, wiggling
the connector will help break through this rust and make a proper connection. If
the reader still doesn't power up retry the reader on an alternative vehicle to
make sure it is working.
After the reader has powered up,
follow the prompt which will include: Read Codes, Clear Codes, and MIL Status,
I/M Data, Freeze Frame Data and Code Review. You want to select "Read Codes".
This will allow the reader to configure a connection from the vehicle’s computer
and accept the error code for display on the reader. Sometimes the data can be
incomplete giving you a
P1000 which means the computer is unable to give codes.
There are two modes
the computer operates in, open and closed loop. If the computer is unable to
switch into closed loop and make adjustments to the engine management system
there is no way for it to tell if anything is wrong hence the P1000 code, more
on that toward the bottom of this article.
Grasp the scanner or code reader
firmly while using the up and down arrows to select and highlight in the prompt,
"Read Codes" and then push the enter button once. This will initiate the code
reader gathering sequence while it communicates with the vehicles computer this
can take up to 20 seconds to complete.
Your vehicle’s computer will then deliver all trouble codes stored in its
error memory and transfer them into the code reader or scanner display. If the
reader or scanner "hangs" on the "working" screen turn the ignition key off and unplug the reader from the ALDL
connector, wait a few seconds and plug it back in and turn the ignition switch
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(s) if there are multiple codes stored,
it will say 1 of 2, which is an indication of more than one code is present.
This will be displayed at the top of the screen on the right side.
Next, 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 telling you which denotes
the system or sensor that has malfunctioned. In this case a PO336 code is
telling us that the crankshaft angle sensor has failed or has failed
intermittently which causes the engine to stall
or not start
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 either turned on or on during the repair, or if the repair
has been made and you want to clear the trouble codes, push the reader or
scanner erase button firmly.
It will then confirm the clearing by asking you to select the up arrow for
yes and the down arrow for no, push the up
arrow. After pushing the button the reader will erase all codes present in the
The reader will then present an option to recheck the system to make sure the
codes have been cleared and there are no present problems with all monitored
systems. The code reader or scanner will then display a pass message reading if
no problems are detected. To be clear this pass state might be temporary if a problem still exists which will
only show up after a while of driving your vehicle, or the check engine light
will come back on immediately if a hard code problem is detected.
A hard code is when the ignition key is first turned to the on position and engine ran for a
few seconds, compared to a regular code which can take a few cycles of the
vehicle being ran and then turned off and then ran again before it shows up.
Once you have finished replacing the
sensor or fixing the vacuum leak (torn hose) and have cleared the codes with the
code reader or scanner, simply turn the ignition key to the off position, the
instrument cluster warning lights should be off.
Then, grasp the connector firmly and
unplug the scanner or code reader connector plug by pulling it gently downward
to separate it from the ALDL data port. Replace the cover of the port if
equipped to prevent any corrosion causing moisture that could cause damage to
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 I
When you have retrieved your trouble codes and would like a more detailed
definition or more information about a particular code.
Most 1996 and newer vehicles utilize an ALDL connector port which is
used to connect a reader for code retrieval. In vehicle's pre 1996 it was up to
the individual automobile manufactures to design their own system for reading
codes. This is why each method is unique from one make of vehicle to the next.
If you have a vehicle that is pre 1996 and would like to know to
retrieve and gather check engine light trouble codes along with their
definitions. Learn more
When this warning light is on the
vehicle's computer system is in limp mode, which means the system is not
running at optimal performance which results in lower power output and
diminished gas mileage.
Once the codes have been cleared, the computer will start testing
through a series of system checks called "Monitors". These sets of monitors are
designed to check engine and emissions systems such as the ignition, fuel
delivery, catalytic converter efficiency and EVAP emission systems to make sure
they are working properly.
Each monitor has its own set of checks and balances
that can take anywhere from 5 miles to 25 miles depending on the automobile
manufactures design. All monitors must be confirmed as okay before the vehicle
can pass emissions testing, this is a big deal in states like California. If the
computer senses a problem, the check engine or service engine light will
If you have any question about the check engine or service engine soon light
or have any car repair questions please
ask our team of certified mechanics
for FREE, we are happy to help you.