Home Page
Car Parts
Tires
Car Answer Sites
Car Information Sites
Interesting Articles
Trouble Codes
When your auto's "check engine light" comes on you can pound on the dashboard all you want hollering "Why Always Me". Is it the car or is it you? Read on.
If the "Check Engine" or "Service Engine Soon" light on your auto comes on it does not mean you have to panic. Take stock of the events that were happening when it came on, if possible. For example, does the engine run rough and misfire, is the speedometer not working, do you smell a rotten egg odor, is there a loss of power or maybe you just got gas a few days ago. These are some of the things that will trigger this light.
If the engine runs rough and misfires you should go to the auto dealer for your brand of vehicle as soon as possible. This problem may be caused by a faulty spark plug, wire, or coil. You should not drive for any extensive time with these symptoms because the catalytic converters may become damaged. If the speedometer does not work it may just be a speed sensor problem which may also affect the shift pattern of the transmission. This should also be checked as soon as possible. A rotten egg odor or any strange exhaust odors are most likely emission related problems such as a rich or lean running condition possibly triggered by a bad O2 sensor or something causing the O2 sensor to react trying to compensate for a problem. This should also be checked fairly soon. The most common problem for a "check engine" light is a missing or loose gas cap. This will not cause any driveability problems.
If your auto develops a "check engine" light shortly after getting gas check and see if the cap is tight and that the retaining strap is not wedged underneath it. When refueling your auto makes sure you hear several clicks when the attendant or you put the cap back on. Do not leave the engine running or have the ignition key in the on position when refueling. This too will cause the light to come on. If your cap was loose just tighten it and within a few drive cycles the computer should be happy and turn the light off. If not a trip to your repair shop is in order to scan the computer for fault codes. Most owners' manuals will show the extent of warranty for these emission control problems. You may be pleasantly surprised at the coverage.
Don't panic, just use common sense to have these problems corrected. Rarely does an auto have to be towed to the shop for this light.
OBD-II
(On
board diagnostics) is
a system used in automobiles to monitor various
components of the vehicle, detect malfunctions, and store the
information in the vehicle’s computer
to be recovered at a later time by using a scanner. When the computer
finds a
fault it will illuminate the “check engine light”.
The “II” in OBD-II denotes
the second and most current version of this technology and has been in
use
since 1995.
At
first there were few standards and each
manufacturer had their own systems and signals. In 1988, the Society of
Automotive
Engineers (SAE) set a standard connector plug and set of
diagnostic
test
signals. The EPA adapted most of their standards from the SAE on-board
diagnostic programs and recommendations. OBD-II is an expanded set of
standards
and practices developed by SAE and adopted by the EPA and CARB
(California Air
Resources Board) for implementation by
Here is
a breakdown of what each digit of the code means:
1st
digit
P
= powertrain
B
= Body
C
= Chassis
2nd digit
0 = Standard
1
= Manufacturer specific
3rd digit
1 = Emission management
2
= Injector circuit
3
= Ignition
4
= Auxiliary emission
5
= Vehicle speed & idle control
6
= Computer & output circuit
7
= Transmission
Since
this
website is designed to help the average “do it
yourself” person in trying to
diagnose and/or repair their
own vehicle I will address only the most
common
and easily repairable trouble codes. I mainly want to avoid total
confusion and
not clutter this site with endless problems and solutions that can only
be
repaired by a professional.
You
will
however need to use an OBD-II scanner. For a list of most OBD-II codes
scroll
to the bottom of this page.
There are more codes than most people
realize.
P0100 Mass
or Volume Air Flow
Circuit Malfunction
P0101 Mass
or Volume Air Flow Circuit
Range/Performance Problem
P0102 Mass
or Volume Air Flow Circuit Low Input
P0103 Mass
or Volume Air Flow Circuit High Input
P0104 Mass
or Volume Air Flow Circuit Intermittent
Look for poor electrical connections at the MASS air flow sensor and the TPS sensor. Loose, corroded, rusted, ground connections at the engine and body. . Loose air tubes, broken vacuum hoses, vacuum leak at intake gaskets, clogged air filter and anything related to air intake.
P0109
Intake Air
Temperature
Circuit Malfunction
P0111 Intake
Air Temperature Circuit
Range/Performance Problem
P0112 Intake
Air Temperature Circuit Low Input
P0113 Intake
Air Temperature Circuit High Input
P0114 Intake
Air Temperature Circuit Intermittent
Look for poor connection at IAT sensor. Usually found on air filter box or air tubes to the engine. These sensors fail more often than others.
P0115 Engine
Coolant Temperature
Circuit Malfunction
P0116 Engine
Coolant Temperature Circuit
Range/Performance Problem
P0117 Engine
Coolant Temperature Circuit Low Input
P0118 Engine
Coolant Temperature Circuit High Input
P0119 Engine
Coolant Temperature Circuit
Intermittent
This sensor can be anywhere on the engine and is subject to easy failure and electrical connector corrosion. Check to see if radiator is full (check cold only) and no coolant leaks.
P0130
through P0167 are
all 02 sensor related. Common problems are
bad connections, wires
burnt by exhaust pipes, faulty sensors, and in some cases blown fuses.
P0170 Fuel
Trim Malfunction (Bank
1)
P0171 System
too Lean (Bank 1)
P0172 System
too Rich (Bank 1)
P0173 Fuel
Trim Malfunction (Bank 2)
P0174 System
too Lean (Bank 2)
P0175 System
too Rich (Bank 2)
Check
for vacuum leaks, low or high fuel pressure, dirty fuel, clogged fuel
filter,
clogged air filter, worn spark plugs, bad pcv valve, and any general
maintenance items.
P0200 Injector
Circuit Malfunction
P0201 Injector
Circuit Malfunction - Cylinder 1
P0202 Injector
Circuit Malfunction - Cylinder 2
P0203 Injector
Circuit Malfunction - Cylinder 3
P0204 Injector
Circuit Malfunction - Cylinder 4
P0205 Injector
Circuit Malfunction - Cylinder 5
P0206 Injector
Circuit Malfunction - Cylinder 6
Check
for bad electrical
connections, bad grounds, clogged injectors, and possibly a bad
computer.
P0300 Random/Multiple
Cylinder Misfire Detected
P0301 Cylinder
1 Misfire Detected
P0302 Cylinder
2 Misfire Detected
P0303 Cylinder
3 Misfire Detected
P0304 Cylinder
4 Misfire Detected
P0305 Cylinder
5 Misfire Detected
P0306 Cylinder
6 Misfire Detected
With
these codes the odds are your engine is miss-firing and running rough.
Check
for poor connections at the coils, bad coil/coils, bad ignition wires,
bad
spark plugs, low compression in the effected cylinder, injector
problems, timing
belt
off a few teeth, bad gas, clogged
exhaust or catalytic converter, bad computer. Usually
these codes are just a bad spark plug
or ign wire but it can get
very complicated.
P0440 Evaporative
Emission
Control System Malfunction
P0441 Evaporative
Emission Control System Incorrect
Purge Flow
P0442 Evaporative
Emission Control System Leak
Detected (small leak)
P0443 Evaporative
Emission Control System Purge
Control Valve Circuit Malfunction
P0444 Evaporative
Emission Control System Purge
Control Valve Circuit Open
P0445 Evaporative
Emission Control System Purge
Control Valve Circuit Shorted
P0446 Evaporative
Emission Control System Vent
Control Circuit Malfunction
P0447 Evaporative
Emission Control System Vent
Control Circuit Open
P0448 Evaporative
Emission Control
System Vent Control Circuit Shorted
P0449 Evaporative
Emission Control System Vent
Valve/Solenoid Circuit Malfunction
P0450 Evaporative
Emission Control System Pressure
Sensor Malfunction
P0451 Evaporative
Emission Control System Pressure
Sensor Range/Performance
P0452 Evaporative
Emission Control System Pressure
Sensor Low Input
P0453 Evaporative
Emission Control System Pressure
Sensor High Input
P0454 Evaporative
Emission Control System Pressure
Sensor Intermittent
P0455 Evaporative
Emission Control System Leak
Detected (gross leak)
These
are the most common reasons for the check engine light to be on. Check
that the
gas cap is on tight (several clicks) and that the retaining strap is
not jammed
under it. Other problems can be a bad gas cap, split hose in the evap
system,
clogged canister, clogged or jammed canister close/vent valve, purge
solenoid
not working properly or vacuum leak going to it, electrical connectors
or bad
grounds, or a bad computer. This is another one of those problems that
can be easy to repair or it can turn
into a
nightmare.
If you go to this link you will find most other "P" codes but for the sake of the average person trying to repair their own vehicle I think I have covered the basics. There is much help to be gotten either from books or searching online but the person doing their own repairs should have above average expertise to avoid causing unnecessary damage to their vehicle.
Back to Top