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2003 camery engine light on. Can't find anything wrong with it.  Engine running rich. Help!  

if the check engine light is on...... there will be a trouble code...   you will need to plug in an OBD2 code reader to access the code... or a scan tool to access the code then examine the live data stream associated with the trouble code..


warning.. just because the trouble code describes an item... its actually describing a circuit..    just replacing the named part.. does not always fix it..   each code goes to a trouble shooting page in the repair manual...  where you can look at the page.. follow the trouble shooting chart.. then examine the live data stream with the scan tool to determine if the sensor is bad.. or something else is causing the sensor to create a signal that is out of the normal range expected by the computer...


there is a neat function of OBD2... when the check engine light turns on..  the computer on your car stores a snap shot of data of what the car was doing when the code set... this allows a mechanic or car owner with a scan tool to know just what was happening..


be sure that if you go to a mechanic or a dealership.. that they give you the actual codes retrived from your car on the paper work...  so you don't end up paying for the same code again and again and again...

some parts stores will come out and read your codes ...  

harbor freight tools stores sell a scan tool #98614 for $119 or $129 which will let you do most of the diagnostic.. for about the same price as the dealership charges ..

if you can get the  codes... post them.. with which motor you have.....


you will also want to pick up a camry factory service manual.. in print.. or one of the online versions from alldatadiy.com or eautorepair.net  

We have had 3 toyota dealers check it out they replaced a sensor then a hose with a crack in it and they say it is running rich and there is nothing wrong with it.  It is a 8cylinder xle.   We would like to sell it but no one is going to buy it with the engine light on.  It has never caused any trouble until this engine light came on.It is now at a service place and they are the ones who changed the hose and now the light is back on.  Thank you all for your in put. Anything else  you all know?  Thanks again.  

We have had 3 toyota dealers check it out they replaced a sensor then a hose with a crack in it and they say it is running rich and there is nothing wrong with it.  It is a 8cylinder xle.   We would like to sell it but no one is going to buy it with the engine light on.  It has never caused any trouble until this engine light came on.It is now at a service place and they are the ones who changed the hose and now the light is back on.  Thank you all for your in put. Anything else  you all know?  Thanks again.  

waynep7122:
if the check engine light is on...... there will be a trouble code...   you will need to plug in an OBD2 code reader to access the code... or a scan tool to access the code then examine the live data stream associated with the trouble code..


warning.. just because the trouble code describes an item... its actually describing a circuit..    just replacing the named part.. does not always fix it..   each code goes to a trouble shooting page in the repair manual...  where you can look at the page.. follow the trouble shooting chart.. then examine the live data stream with the scan tool to determine if the sensor is bad.. or something else is causing the sensor to create a signal that is out of the normal range expected by the computer...


there is a neat function of OBD2... when the check engine light turns on..  the computer on your car stores a snap shot of data of what the car was doing when the code set... this allows a mechanic or car owner with a scan tool to know just what was happening..


be sure that if you go to a mechanic or a dealership.. that they give you the actual codes retrived from your car on the paper work...  so you don't end up paying for the same code again and again and again...

some parts stores will come out and read your codes ...  

harbor freight tools stores sell a scan tool #98614 for $119 or $129 which will let you do most of the diagnostic.. for about the same price as the dealership charges ..

if you can get the  codes... post them.. with which motor you have.....


you will also want to pick up a camry factory service manual.. in print.. or one of the online versions from alldatadiy.com or eautorepair.net

We have had 3 toyota dealers check it out they replaced a sensor then a hose with a crack in it and they say it is running rich and there is nothing wrong with it.  It is a 8cylinder xle.   We would like to sell it but no one is going to buy it with the engine light on.  It has never caused any trouble until this engine light came on.It is now at a service place and they are the ones who changed the hose and now the light is back on.  Thank you all for your in put. Anything else  you all know?  Thanks again.  

waynep7122:
if the check engine light is on...... there will be a trouble code...   you will need to plug in an OBD2 code reader to access the code... or a scan tool to access the code then examine the live data stream associated with the trouble code..


warning.. just because the trouble code describes an item... its actually describing a circuit..    just replacing the named part.. does not always fix it..   each code goes to a trouble shooting page in the repair manual...  where you can look at the page.. follow the trouble shooting chart.. then examine the live data stream with the scan tool to determine if the sensor is bad.. or something else is causing the sensor to create a signal that is out of the normal range expected by the computer...


there is a neat function of OBD2... when the check engine light turns on..  the computer on your car stores a snap shot of data of what the car was doing when the code set... this allows a mechanic or car owner with a scan tool to know just what was happening..


be sure that if you go to a mechanic or a dealership.. that they give you the actual codes retrived from your car on the paper work...  so you don't end up paying for the same code again and again and again...

some parts stores will come out and read your codes ...  

harbor freight tools stores sell a scan tool #98614 for $119 or $129 which will let you do most of the diagnostic.. for about the same price as the dealership charges ..

if you can get the  codes... post them.. with which motor you have.....


you will also want to pick up a camry factory service manual.. in print.. or one of the online versions from alldatadiy.com or eautorepair.net

We have had 3 toyota dealers check it out they replaced a sensor then a hose with a crack in it and they say it is running rich and there is nothing wrong with it.  It is a 8cylinder xle.   We would like to sell it but no one is going to buy it with the engine light on.  It has never caused any trouble until this engine light came on.It is now at a service place and they are the ones who changed the hose and now the light is back on.  Thank you all for your in put. Anything else  you all know?  Thanks again.  

2003 Toyota Camry:
Available engines
         o 4 Cylinders E 2.4L MFI DOHC
         o 6 Cylinders F 3.0L SFI DOHC


Catalyst Monitor


A downstream (post-catalyst) Heated Oxygen Sensor (HO2S-12) is used to provide the additional signals needed to monitor the efficiency of the three-way catalyst on these systems. The PCM compares the signals between the upstream (pre-catalyst) and downstream oxygen sensor during stable driving conditions with the engine warm in order to determine the oxygen storage capacity of the catalytic converter.
Catalyst Monitor "Trip" Pattern

The Catalyst Monitor "trip" pattern shown below can be used to validate repair of DTC P0420/P0430 or to "run" the Catalyst Monitor to complete the I/M Readiness Test. Federal models require that the vehicle be driven at a different speed than for California models. If the engine is cold on 2002 models, repeat the test (key off after the test).


Catalyst Monitor Operation

To measure catalyst efficiency, the Catalyst Monitor interprets the signals from the pre-catalyst and post-catalyst oxygen sensors. If the three-way catalyst is operating correctly, the post-catalyst signal will have significantly less activity than the pre-catalyst. Run the engine at 2500 rpm for 3 minutes in P/N and then check the waveforms from both sensors. If the signals are similar, the catalyst may be degraded.



Comprehensive Component Monitor


The Comprehensive Component Monitor (CCM) is an on-board strategy designed to monitor for failures in emission-related electronic components and circuits that provide input or output signals to the PCM. These are systems or devices that are not exclusively monitored by another monitor system. If the PCM detects that an input or output signal is inoperative due to an out-of-range value, open circuit or if an on-board rationality or functionality check fails, the PCM will set a code in memory and activate the MIL.

Tests conducted by the CCM vary depending on the type of hardware, the function of the device and the signal type. Analog signals are checked continuously for opens, shorts and out-of-range values. Some digital signals are checked for both functionality and rationality. These tests require that certain engine conditions be present before the test is performed and that several components are monitored as part of the test. Also, a sensor value can be monitored for change after the PCM sends a command to a device. Here is a list of devices checked by the CCM at key on or engine running.
Input Device Examples


Barometric Pressure Sensor

Brake Switch

Camshaft & Crankshaft Sensors

Clutch Switch (M/T)

Cruise Servo Switch

Engine Coolant Temperature Sensor

EVAP Pressure Sensor

Intake Air Temperature Sensor

Knock Sensor

Manifold Absolute Pressure Sensor

Mass Airflow Sensor

Park Neutral Switch

Transmission Temperature Sensor

Transmission Speed Sensor

Vehicle Speed Sensor


Output Device Examples


EVAP Purge and Vent Solenoids

Idle Air Control Solenoid

Ignition Control System

Transmission Torque Converter Clutch Solenoid

Transmission Shift Solenoids (Solenoid S1, S2 and S3)


EGR System Monitor


The EGR system is used to reduce the amount of NOx emissions by circulating a portion of the exhaust gas through the EGR valve to the intake manifold. The PCM uses the MAP sensor signal to detect an EGR system fault by determining if the signal is too high or too low.



Main Monitors (OBD II Monitors)


A key difference between the first version of On Board Diagnostics (OBD I) and the second version (OBD II) is the use of several PCM controlled monitors contained within the PCM software structure. These monitors perform diagnostic tests required in order to meet specific California Air Resources Board (CARB) and EPA regulations.

Simply stated, an OBD II Monitor is a diagnostic strategy designed to test the operation of an emissions-related component or system. Some OBD II System Monitors accomplish this task directly by monitoring the action of various input and output devices or sensors connected to the PCM. An example of direct monitoring is when the Comprehensive Component Monitor monitors the Engine Coolant Temperature or Intake Air Temperature Sensor inputs.

Other OBD II System Monitors accomplish the task indirectly by monitoring the effects of changes to a system or component. The indirect method may be accomplished through monitoring a change or response in a system. This type of test is done by monitoring the input or output signals of a particular device for an "inferred" change.

An example of indirect monitoring is when the PCM infers correct or incorrect catalyst action using the Catalyst Monitor to sample signals from the upstream or downstream oxygen sensors. This allows the PCM to determine the oxygen storage efficiency of the catalyst.

Some of the Main Monitors run continuously while some run only once per trip. The next few articles explain how the Monitors operate.
Continuous Monitors (Run All The Time)


Fuel Control System - begins when the engine enters closed loop

Misfire Detection Test - begins right after startup


Main Monitors That Run Once Only Per Trip:


Catalyst Efficiency Test - begins in closed loop after certain engine temperature, time and VSS requirements are met

EGR System - begins in closed loop after certain engine temperature, time and VSS requirements are met

EVAP System Test - begins in closed loop after certain engine temperature, time and VSS requirements are met

O2S Test - voltage and response time tests begin in closed loop after engine temperature, time and VSS requirements are met

Secondary AIR System Test - begins in closed loop at off-idle


Note: Once all of the required enable criteria are met, Toyota OBD II systems are programmed to run all the OBD II main monitors once each trip.  

Diagnostic Trouble Code (DTC) Explanation

The number in the hundredth position indicates the specific vehicle system or sub-group in which the failure occurred.


This position should be consistent for P0xxx and P1xxx type codes.

An example of how to interpret an OBD II code is shown in the Graphic to the right.

The Society of Automotive Engineers (SAE) developed the numbers and systems in the list that follows:

P0100 - Air Metering and Fuel System fault

P0200 - Fuel System (fuel injector only) fault

P0300 - Ignition System or Misfire fault

P0400 - Emission Control System fault

P0500 - Idle Speed Control, Vehicle Speed Sensor fault

P0600 - Computer Output Circuit (relay, solenoid, etc.) fault

P0700 - Transaxle, Transmission faults

Note: The first and tenth digits indicate the type of Emission System that has failed.
OBD II Warmup Cycle

Once a MIL is off, the trouble code will remain in memory until 40 warmup cycles are completed without the same fault reoccurring.

A warmup cycle is defined as a trip that includes a change in engine temperature of at least 40F, and where the engine tempe rature reaches at least 160F.  

now...   how do you know the engine is running rich..???

excessive smoke from the exhaust???

there are many things that can make it run rich and won't set a code..

the fuel pressure regulator could have failed and is leaking gasoline directly into the intake manifold though the vacuum hose..  

this is just one thing... there are dozens more.


start with code numbers...    P0000 code numbers..

why is the check engine light on..   must be a code...

now.. when you turn the key on..  the check engine light should be on..  when you start the engine.. the check engine light should be on for 2 to 5 seconds.. then go off.. this is bulb check.. to prove that you just have not removed the bulb..  

find a local chain auto parts stores.. some will come out and read your codes..  for free...

start there....