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). 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 ÷ 12 V), however, it becomes decisive in the diagnosis of elements that produce low-voltage signals, such as, for example, an oxygen sensor, where it is a matter of measuring fractions of a volt.
The most convenient devices for diagnosing engine control systems of modern car models are manual scanner-type readers. First generation scanners are used to read fault codes for OBD-I systems. 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 in car accessories stores.
Other types of scanners are also available, designed to be read from the memory of the onboard processor by direct connection to the diagnostic connector of the main braid of the vehicle's electrical wiring.
General description of the OBD system
All models described in this manual are equipped with an on-board diagnostic system (OBD). On models 1993 and 1994 issue the OBD-I system is used, since 1995 all cars began to be equipped with second-generation diagnostic systems (OBD-II).
The main element of both systems is the onboard processor, more often called the electronic module for controlling the functioning of the power unit (RSM). The PCM is the brain of the engine management system. The initial data is fed to the module from various information sensors and other electronic components (switches, relays, etc.). Based on the analysis of the data coming from the information sensors and in accordance with the basic parameters stored in the processor memory, the PCM generates commands for the operation of various control relays and actuators, thereby adjusting the operating parameters of the engine and ensuring maximum efficiency of its output with minimum fuel consumption.
Engine management/emission control system components are subject to a special extended warranty. You should not attempt to independently diagnose PCM failures or replace system components before the expiration of these obligations - contact Toyota authorized service stations.
Information sensors
Camshaft position sensor (SMR) - The sensor generates information signals, based on the analysis of which the PCM determines the current valve timing and engine speed, using the information received when controlling the injection sequence and ignition of the air-fuel mixture in the combustion chambers.
Sensor (And) crankshaft position (TFR) - On all models since 1995 vol. two SKR sensors are used, while on earlier models only one such sensor was used. The signals coming from the sensors are used by the PCM as a reference when determining the engine speed and the TDC positions of the piston of each of the cylinders. Based on the information received, the PCM controls the sequence of injection and ignition of the air-fuel mixture in the combustion chambers. In OBD-II systems, the signals generated by the TFR sensors are also used in the diagnosis of failures of the power unit.
Engine coolant temperature sensor (EATING) - Based on the information coming from the sensor, the PCM makes the necessary adjustments to the composition of the air-fuel mixture and the ignition timing, and also controls the operation of the EGR system.
EGR temperature sensor - Information coming from the sensor is used to determine the intensity of exhaust gas recirculation into the intake tract of the engine.
Fuel temperature sensor - PCM uses the information provided by the sensor when diagnosing system component failures.
intake air temperature sensor (IAT) - The PCM uses information from the IAT sensor to make adjustments to injection parameters, ignition timing settings, and to control the operation of the EGR system.
Knock sensor - The sensor is a piezoelectric element that responds to changes in the intensity of engine vibrations. Based on the analysis of the information coming from the sensor, the PCM performs adjustments to the ignition timing in order to timely eliminate the detonation of the air-fuel mixture that occurs in the combustion chambers, which is fraught with premature wear of the internal components of the engine.
Absolute pressure sensor in the pipeline (IDA) (models since 1996 issue.) - The sensor monitors variations in the depth of vacuum in the intake manifold associated with changes in crankshaft speed and engine load, and converts the information received into an amplitude signal. The information from the sensor is used by the control module in diagnosing engine failures.
Air mass meter (MAF) - The MAF sensor determines the volume and weight parameters of the air flow entering the intake pipeline. A filament is used as a sensitive element in the sensor. The PCM uses the information provided by the MAP and IAT sensors to make fine adjustments to the injection parameters.
Oxygen sensor (λ probe) - The sensor generates a signal whose amplitude depends on the ratio of the amount of oxygen (ABOUT2), contained in the exhaust gases of the engine and the outside air. Based on the information coming from the sensor, the PCM determines the parameters of the air-fuel mixture, promptly enriching or depleting it.
Power steering fluid pressure switch (PSP) - Based on the information coming from the PSP sensor-switch, the PCM provides an increase in idle speed (by actuating the IAC valve) in order to compensate for the increasing loads on the engine associated with the operation of the power steering during maneuvers.
Throttle position sensor (TPS) - The sensor is located on the throttle body and connected to the throttle shaft. Based on the amplitude of the TPS signal output, the PCM determines the throttle opening angle (controlled by the driver from the gas pedal) and adjusts the fuel supply to the inlet ports of the combustion chambers accordingly. The failure of the sensor, or the weakening of its fastening, leads to interruptions in injection and violations of the stability of the idle speed.
Vehicle speed sensor (VSS) - As its name implies, the sensor informs the processor about the current vehicle speed.
Other parameters controlled by the PCM - In addition to the sensors listed above, the PCM also receives additional information about the functioning of various components and systems that determine the performance of the engine. Other systems and components managed by PCM include the following:
- a) Air conditioning system;
- b) ABS;
- c) Accumulator battery (output voltage);
- d) EVAP system;
- e) Ignition switch;
- f) Launch enable switch;
- g) Ground circuits;
- h) Transmission operation control system.
Executive devices
The relay for controlling the operation of the K / V clutch - PCM switches off the K / V compressor during intensive acceleration.
Pilot lamp "Check engine" - The PCM turns on this warning lamp when there is a malfunction in the engine management system.
The cooling fan control relay - PCM controls the operation of the cooling fans based on the analysis of signals from the coolant temperature sensor.
EGR Vacuum Control Solenoid Valves - Pre-1999 Models The PCM controls the opening degree of the EGR vacuum valve through a special intermediate solenoid valve.
EGR valve - On 1999 models. The PCM controls the EGR flow through the electronic EGR valve.
Canister Purge Valve - This solenoid valve, actuated by the PCM, purges the EVAP system's charcoal canister, expelling accumulated fuel vapors into the engine intake tract.
Fast idle control solenoid valve - This valve is used on models from 1995 onwards. and serves to increase idle speed in cold weather. In fact, this valve acts as an air damper on carburetor models.
Powertrain Front Mount - On some models, the PCM also controls the stiffness of the front engine mount based on vehicle speed. Vibration is minimized by selecting one of two support settings.
Fuel injection injectors - The PCM ensures that each injector is individually activated according to the established firing order. In addition, the module controls the duration of the opening of the injectors, determined by the width of the control pulse, measured in milliseconds, which determines the amount of fuel injected into the cylinder. More detailed information on the principle of operation of the injection system, replacement and maintenance of injectors is given in Chapter Power and exhaust systems.
Fuel Pump Relay - The relay is activated by the control module when the ignition key is turned to the START/RUN position. When the ignition is turned on, the relay energizes the fuel pump, which provides a pressure increase in the path of the car's power system. For more information on the location and function of the relay, see Chapters Onboard electrical equipment and Power and exhaust systems.
Idle speed control valve (IAC) - The IAC valve controls the amount of air bypassing the throttle when the throttle is closed or in the idle position. The opening of the valve and the formation of the resulting air flow is controlled by the PCM.
Oxygen Sensor Heater - This device is controlled by the PCM. The heater quickly heats up the l-probe to normal operating temperature.
Power transistor - The transistor amplifies the ignition signal generated by the PCM and at the right time produces an instantaneous ground to the mass of the primary circuit of the ignition system, which causes the generation of an HV signal generated by the coil in the secondary circuit of the system (ami) directly to the spark plugs (see chapter Engine electrical equipment).
Power valve operation control solenoid - On 1993 and 1994 models. issue the operation of the power valve is controlled by the PCM by means of a special electromagnet.
Transmission Function Control Module (TCM) - The TCM, being a control module separate from the PCM, receives signals from various information sensors, such as VSS, start enable switch, turbine shaft speed sensor, TPS, CMP, etc., and uses the received data when determining the moment of gear shifting AT, the required pressure in the path and the moment of blocking the rotation converter.
Reading trouble codes
If a malfunction is detected that repeats in a row during the spirit of trips, the PCM issues a command to turn on the warning lamp built into the instrument panel "Check engine", also called the failure indicator. The lamp will remain lit until the disturbance disappears and does not reappear for three or more trips.
Reading trouble codes in the OBD-II system can be done in two ways. In the first case, it is necessary to provide access to the PCM in order to switch the selector to display codes using diagnostic lamps / warning lamp "Check engine". The PCM must be removed from its support bracket (without disconnecting the wiring) and follow the instructions below.
Models 1993 and 1994 issue
- a) Turn on the ignition (without starting the engine). Pilot lamp "Check engine" on the instrument panel should remain on, which confirms that power is being supplied to it from the PCM and that the lamp itself is working.
Violation of the procedure described below may lead to accidental clearing of PCM memory!
- b) Using a screwdriver, turn the selector on the PCM wall clockwise as far as it will go. The diagnostic lamps should start flashing, - after three flashes, turn the selector counterclockwise as far as it will go;
- c) Carefully observe the functioning of the diagnostic lamps. The red LED is used to display the first digit of the fault code, the second digit of the code is illuminated by a green diode. For example, code (TPS chain) 43 will look like this: four flashes of a red diode, then three flashes of green. The absence of violations detected by the system is indicated by the display of code 55 (see below in this Section a map of fault codes);
- d) When the ignition is turned on again after turning it off while reading the codes, the system automatically cancels the results of the previous search and the reading procedure must be restarted. Note: Starting the engine automatically disables access to the self-diagnosis system.
Models since 1995 vol.
- a) Turn on the ignition (without starting the engine). Pilot lamp "Check engine" on the instrument panel should remain on, which confirms that power is being supplied to it from the PCM and that the lamp itself is working.
Violation of the procedure described below may lead to accidental clearing of PCM memory!
- b) Using a screwdriver, turn the selector on the PCM wall clockwise as far as it will go. The diagnostic lamps should start flashing, - after three flashes, turn the selector counterclockwise as far as it will go;
- c) Carefully observe the operation of the control lamp "Check engine". The lamp will flash the first digit of the code in a series of long (approximately 0.6 s) flashes, then, after a 2-second pause, it will begin to display the second digit of the code in the form of a series of short (by 0.3 s) glimpses. In order to determine the highlighted code, write down the number of flashes of each series, for example, code 0403 (TPS chain) will look like this: 4 long flashes, then, after a pause, three short ones. The absence of violations detected by the system is indicated by the display of code 0505 (see below in this Section a map of fault codes);
- d) When the ignition is turned on again after turning it off while reading the codes, the system automatically cancels the results of the previous search and the reading procedure must be restarted. Note: Starting the engine automatically disables access to the self-diagnosis system.
The second method involves the use of a special scanner, and is only applicable on models equipped with an OBD-II system (since 1995 issue.). with the help of a scanner, a deeper diagnosis of the engine condition and a fine assessment of its operating parameters can be made. In addition, the scanner allows you to read data frozen by the OBD system at the time of the occurrence of an intermittent failure.
Note. When using a scanner, a different form of writing codes is used, different from that used when reading through a control lamp "Check engine". In this case, a prefix like P0 or P1 is used (see the relevant section of the code map table). In the absence of a scanner at hand, the diagnosis of unstable violations of the engine control system can only be carried out in a car service workshop.
Clearing ECM/PCM Memory
After the violations identified during the diagnostic process are eliminated, the PCM memory should be cleared of the fault codes recorded in it.
You should not clear the memory by disconnecting the negative wire from the battery - this will also lead to a loss of basic parameters and a violation of the stability of the idle speed for the first time after starting the engine.
Note. When using the scanner in OBD-II systems, set the device to "CLEARING CODES" and act in accordance with the manufacturer's instructions.
Models 1993 and 1994 issue
- a) Read the codes of malfunctions written down in memory of system;
- b) Wait at least two seconds, then turn the selector on the PCM wall all the way clockwise - the LEDs should start flashing;
- c) After four flashes of the diodes, turn the selector counterclockwise as far as it will go;
- d) Switch off the ignition.
Models since 1995 vol.
- a) Read the codes of malfunctions written down in memory of system;
- b) Wait at least two seconds, then turn the selector on the PCM wall fully clockwise;
- c) Wait at least two more seconds and turn the selector counterclockwise as far as it will go;
- d) Switch off the ignition.
The memory must always be cleared before starting the engine for the first time after replacing the engine management system components. If a fault code of any of the information sensors was recorded in the module memory, then if, after replacing the failed component, the engine is started without clearing the memory, the old code will remain in effect and the system will switch to the basic settings mode, excluding the new sensor from the list of working components.
Note. During the first 15÷20 seconds after the first start, the engine speed may remain unstable, which is associated with the recovery of the processor performance.
Identification of codes of malfunctions of the engine management system
The Specifications provides a complete map of possible fault codes, not all of which may occur for a particular vehicle configuration.