Tech Notes:

Diagnostic Trouble Codes and Possible Causes

For Toyota's with electronic fuel injection utilizing the Toyota EFI
or TCCS engine management system.

 
    Toyota's with the electronic fuel injection utilize the Toyota EFI or TCCS engine management system.  This system helps to enhance the performance, emissions, and drivability of the vehicle.  The Self-Diagnostic System, which monitors engine operations, is just one of the features of this system.  The Check Engine light will appear when a particular sensor or input varies out of the specified operation parameters.
 
     The check engine light alerts the user that there is a possible problem in the EFI / TCCS Engine Control Unit.  This is an indication of a problem in the engine management system.  A code that pinpoints a possible component in the EFI / TCCS system may be stored in the ECU at this time.  The problem can be narrowed down to a number of possible causes just by checking the trouble codes at this time.  The self-diagnostic system allows the user to zero in on the possible fault.
 
     The chart on the following page contains 1 and 2 digit trouble codes that will help to diagnose problems in the EFI / TCCS system.  The chart also contains possible causes of the problem.  Keep in mind this is a tool to help narrow down the problem and may not be exact.  Other components failures have been known to cause similar symptoms that can hide the actual fault.
 
     Be sure to do a complete inspection before you do any repairs on the computer of the vehicle.  The last step to an engine diagnose should always be a computer interrogation.
    
     Remember to be cautious with the electrical system within the vehicle.  Serious injury can occur if the user or technician is now careful.  the electrical system can be damaged if not careful; water and static electricity can easily cause damage.  Also keep in mind that the ignition system does put out high voltage.  Always put your safety first when dealing with these components of your vehicle.
 
     The diagnostic trouble codes are easy to read.  All you need is a simple paperclip to short the check connectors of the diagnostic connector.  There are two different types of diagnostic connectors.  For those of you who own an early model vehicle, check on the inner-left fender well for a round green connector close to the air cleaner.  With the ignition key on, but the motor off, jump the two terminals in the connector.  On the later models, 87 and newer, there is a multiple terminal "Diagnostic" connector which is located in the engine compartment on the right fender.  Look for a small rectangular shaped gray box.  In order to get the codes from this connector you need to jump the "TE1" and "E1" terminals.  To find the terminals, look at the inside of the diagnostic connector.  Here you will find a schematic, which labels the connector pinouts.  There is also a (VECI) emissions decal located under the hood, which also outlines the terminals.
 
     The trouble codes will appear as flashes of the check engine light.  When reading the codes, make sure your foot is OFF the accelerator, the ignition key ON and the engine is OFF.   There are two different codes that will appear, one digit and two digit.  The one digit codes have and approximate 4.5 sec. delay between flashes with the check engine light illuminating for around a half second.
 
     On the two digit codes you will have a 2.5 sec. delay between them.  Here are some example codes to follow.  A code two flashes the check engine light two times in little over one second; I I.  When multiple codes are stored, like a code 2 and code 4, the light will flash the following; ....I I....I I I I.  Two digit codes are real similar, but will flash the light with the first number first then the second dumber last.  For example, a code 12 will flash; I....I I.  A code 24 is; I I....I I I I.  The examples are a little crude but you get the idea.  (In these examples, the ..I.. represents the check engine flashing once.)
 
   
 An ECI failure is not common, although many possible faults might seem to point to the EFI system.  Only if all diagnoses points to a faulty ECU should it be replaced.  Typically EFI problems result from poor grounds, shorted wiring and bad connections at sensors.
 
     For more comprehensive diagnostic information and electrical wiring diagrams, carefully consult your factory repair manual.


 
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