Note. All models in question are equipped with OBD II systems (second generation), which require a special scanner to read the data from the memory. In view of the foregoing, reading fault codes from the memory of the OBD II system should be entrusted to specialists from a branded service station that has all the necessary diagnostic equipment. All OBD II equipped models use five-digit diagnostic codes, some of which are given in the text of this Section, more detailed information can be obtained from Toyota representatives.
Information about diagnostic tools
Checking the correct functioning of the components of the injection systems and reducing the toxicity of exhaust gases is carried out using a universal digital meter (multimeter) (refer to accompanying illustration).
The use of a digital meter is preferred for several reasons. Firstly, it is quite difficult for analog devices to (sometimes impossible), determine the result of the indication with an accuracy of hundredths and thousandths, while when examining circuits that include electronic components, such accuracy is of particular importance. The second, no less important, reason is the fact that the internal circuit of a digital multimeter has a fairly high impedance (the internal resistance of the device is 10 million ohms). Since the voltmeter is connected in parallel to the circuit under test, the measurement accuracy is the higher, the less parasitic current will pass through the device itself. This factor is not significant when measuring relatively high voltage values (9-12V), however, it becomes decisive in the diagnosis of elements that produce low-voltage signals, such as, for example, a lambda probe, where we are talking about measuring fractions of a volt.
The most convenient devices for diagnosing engine control systems of modern car models are manual scanner-type readers (refer to accompanying illustration). Before use, the reader should be checked for compliance with the model and year of manufacture of the vehicle being checked. Some scanners are multifunctional, due to the possibility of changing the cartridge depending on the model of the car being diagnosed (Ford, GM, Chrysler, etc.), others are tied to the requirements of regional authorities and are intended for use in certain areas of the world (Europe, Asia, USA, etc.).
With the introduction of a second-generation on-board diagnostic system that meets the latest environmental legislation (OBD-II) Readers of a special design began to be produced. Some manufacturers have launched scanners designed for use by amateur mechanics at home - ask at car accessories stores.
Note. Despite the fact that reading fault codes in OBD II systems is not possible without the use of a special scanner, below, in Section Information sensors - general information and function check a description of some of the simplest checks of individual components of the system is given.
General information
Layout of components for engine management and emission control systems on models with a V8 engine
1 - VSV vapor pressure sensor; 2 - Vapor pressure sensor; 3 - Start enable switch (AT); 4 - fuel pump ECU; 5 - VSS; 6 - DLC #3; 7 - Sensor-switch of brake lights; 8 - Heated lambda probe (row 1 sensor 2 and block 2 sensor 2); 9 - Main relay EFI; 10 - Heated lambda probe (row 1 sensor 1); 11 - Knock sensor No. 1; 12 - Heated lambda probe (row 2 sensor 1); 13 - Knock sensor No. 2; 14 - CKP sensor; 15 - CMP sensor; 16 - Coolant temperature sensor; 17 - Throttle actuator with electromagnetic clutch; 18 - Accelerator pedal position sensor; 19 - MAF sensor; 20 - DLC #1; 21 - TPS; 22 - Ignition coil; 23 - ECM; 24 - VSV EVAP systems
Electronic injection and emission control systems in the course of their operation during vehicle operation intersect with various other systems responsible for the efficiency of engine output. All of these systems include a set of information sensors and an electronic control module (ECM) (refer to illustration above).
Such systems can be compared in their structure with the central nervous system of the human body, where the role of the brain is played by the control module (ECM), and information sensors act as nerve endings. The sensors send signals to the ECM, which analyzes the incoming information and generates response commands to correct the corresponding operating parameters.
Consider a specific example that allows you to more clearly imagine the principle of the system: a lambda probe mounted in the exhaust system continuously monitors the level of O2 in the exhaust gas stream of the engine. If the oxygen percentage noticeably deviates from some reference value stored in the system memory, the ECM immediately receives the relevant information and, based on its analysis, issues a command to appropriately adjust the duration of the opening of the fuel injectors, thereby adjusting the composition of the air-fuel mixture. The duration of the described procedural cycle is a fraction of a second, which ensures the proper efficiency of the system. As a result, the efficiency of the engine output is constantly maintained at the highest possible level.
Reading OBD-II Trouble Codes
Note. Reading OBD-II trouble codes is only possible using special equipment. The text of this Section contains a far from complete list of codes detected by the system - if necessary, contact the representative offices of the vehicle manufacturer for advice.
In the OBD-II system, five-digit trouble codes are stored in the processor memory (ECM).
The codes stored in the processor memory are read using a special OBD-II scanner, which is connected to the 16-pin DLC 3 diagnostic connector (refer to accompanying illustration). The scanner is a laptop equipped with an interface for connecting to the on-board self-diagnosis system and is an extremely effective tool, allowing not only to read codes, but also to obtain information about the current functioning parameters of information sensors and actuators. The scanner has a rather high cost, which is why it would be wise to entrust the diagnostic procedure to car service specialists.
It should be noted that the on-board self-diagnosis system is not able to detect all possible failures - if necessary, do not hesitate to seek advice from Toyota branded service stations. When searching for reasons for reduced engine efficiency, increased fuel consumption, or increased exhaust emissions (these violations are usually not accompanied by the operation of a warning lamp «Check engine») you should first of all carry out the whole complex of standard checks to identify the causes listed in the Section on diagnosing malfunctions of vehicle systems and components in the introduction to this Manual, and only after that switch to the OBD system.
It should be remembered that the use of OBD-II requires the operator to have a basic knowledge of automotive electronics, failure to follow precautions when handling the ECM and other electronic components can lead to permanent failure of the system.
The table below provides a list of OBD-II diagnostic codes for the most common system failures. If it is not possible to identify and eliminate the cause of the failure on your own, the car should be driven to a service station in order to carry out diagnostics using special diagnostic equipment.
Clearing the OBD-II Memory
To clear the ECM memory, connect a scanner to the system and select the function in the menu layout of its menu «CLEARING CODES» («Deleting codes»). Then follow the instructions displayed on the device, or immediately remove the EFI fuse from its socket in the mounting block for 30 seconds. Alternatively, system memory can be cleared by removing the fuse link (the main fuse of the onboard power supply system), installed near the positive battery terminal (see Onboard electrical equipment) (you can also just disconnect the positive wire from the battery).
Attention! If the stereo system installed in the car is equipped with a security code, before disconnecting the battery, make sure that you have the correct combination to activate the audio system!
Note. Disconnecting the battery also deletes the receiver's favorite radio stations.
Attention! To avoid damage to the ECM, disconnect and connect it only with the ignition off!