Tccs System Toyota 4Runner I

DESCRIPTION

The Toyota Computer Control System (TCCS) is a computerized emission, ignition and fuel control system. The TCCS controls Electronic Fuel Injection (EFI), engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability.

The Electronic Control Unit (ECU) controls the TCCS. The ECU contains preprogrammed information which has all data necessary for maintaining optimum ignition timing under all operating conditions. Input from the various data sensors allows the ECU to deliver spark at exactly the right moment. The ECU controls many engine related systems to constantly adjust engine operation. (Scheme 60)

The TCCS is primarily an emission control system, designed to maintain an ideal air/fuel ratio of 14.7:1 under all operating conditions. When an ideal air/fuel ratio is maintained, the catalytic converter can control carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) emissions.

Computer Control System Schematics. Scheme 60

OPERATION

The TCCS consists of the following subsystems: Electronic Fuel Injection (EFI) system, Data Sensors, Electronic Control Unit (ECU), Electronic Spark Advance (ESA) system, Idle Speed Control (ISC) system, EGR Control, Electronic Controlled Transmission (ECT), Diagnostic System and catalytic converter. (Scheme 61)

ELECTRONIC FUEL INJECTION (EFI)

All models are equipped with a Bosch AFC fuel injection system. An electric fuel pump provides fuel to the fuel pressure regulator. From the regulator, fuel flows under pressure to the fuel injectors. The pressure regulator maintains uniform pressure differential at all times.

The constant pressure differential allows the ECU to control duration of injection. The ECU monitors engine running conditions and calculates injection duration for efficient engine operation.

The ECU activates all injectors at the same time. When the injectors are activated, they provide 1/2 the amount of fuel required for ideal combustion with each engine revolution. For more information, see FUEL INJECTION SYSTEM - BOSCH AFC article in FUEL SYSTEMS.

TCCS Component Locations. Scheme 61

DATA SENSORS

Each sensor furnishes electrical impulses to ECU. The ECU computes fuel delivery and spark timing necessary to maintain desired air/fuel ratio and engine speed. Data sensors are interrelated with each other. Operation of each sensor is as follows

Airflow Sensor

This sensor is mounted within the airflow meter. The sensor measures airflow rate through the airflow meter and sends a proportionate electrical signal to ECU. The ECU uses airflow sensor information for controlling fuel injection duration and spark advance system.

Air Temperature Sensor

Sensor is mounted within the airflow meter. The sensor measures temperature of incoming air and sends an electrical signal to ECU. The ECU uses air temperature information for controlling fuel injection duration.

Throttle Position Sensor (TPS)

The throttle position sensor (TPS) is mounted on throttle body and is directly connected to throttle linkage. The sensor, a rotary potentiometer, signals ECU of changes in throttle valve position. This information is used for controlling fuel injection duration and idle speed control system.

Coolant Temperature Sensor

The coolant temperature sensor is installed in intake manifold. This sensor is a thermistor which converts temperature of engine coolant to electrical signal for use by ECU. The ECU uses coolant temperature information for controlling fuel injection duration, spark advance system, idle speed control system and EGR system.

Oxygen Sensor

The oxygen sensor is installed in exhaust manifold. Output voltage of oxygen sensor varies with oxygen content of exhaust gases. The ECU uses exhaust gas oxygen content information for determining fuel injection duration.

Vehicle Speed Sensor (VSS)

This sensor is mounted in the instrument panel and is a component of the speedometer. Vehicle speed information is used by the ECU for cruise control and electronic control of automatic transmission.

Engine Speed

Engine speed signal information is received from the ignition coil. These signals are used by ECU for fuel injection duration control and spark advance system.

A/C Switch

A signal is sent to ECU when the air conditioner is activated. The ECU requires this input for controlling idle speed during A/C operation.

Neutral/Start Switch

A switch is installed on automatic transmission models to inform the ECU of transmission selection position. This information is used by the ECU to allow starter operation. This information is also relayed to the ECT computer. Manual transmission models are equipped with a clutch switch.

ELECTRONIC CONTROL UNIT (ECU)

The ECU controls all functions of the TCCS. The ECU consists of a printed circuit board enclosed within a metal box. The ECU receives signals from the data sensors and switches. These signals are processed by the ECU for controlling the EFI, ESA, ISC, EGR and ECT systems.

The TCCS has a "fail-safe" feature designed into the ECU. If the ECU malfunctions, a back-up circuit is activated to assist in getting the vehicle to a service facility. During this mode of operation, driveability will be minimal. The "Check Engine" lamp will also be lit when the computer malfunctions.

Electronic Control Unit Electrical Connector ID. Scheme 62

ELECTRONIC SPARK ADVANCE (ESA) SYSTEM

The ECU contains preprogrammed information which has all the data necessary for maintaining optimum ignition timing under all operating conditions. Input from the various data sensors allows the ECU to deliver spark at exactly the right moment.

IDLE SPEED CONTROL (ISC) SYSTEM

Engine idle speed is controlled by the ECU. The ECU contains preprogrammed information which contains specific engine speed values for different engine operating conditions.

The ECU receives signals from such sensors as the coolant temperature sensor and air conditioner sensor. Using this information, the ECU transmits a command signal to the ISC valve in the throttle body.

The ISC valve opens and closes the idle air by-pass to control the amount of air which by-passes throttle valve. The greater the amount of air which is by-passed around the throttle valve, the greater the engine idle speed.

EGR CONTROL

The EGR control system prevents recirculation of exhaust gases when coolant temperature is below 135°F (57°C). The coolant temperature sensor constantly monitors and informs the ECU of coolant temperature. When the temperature is below the specified value, the ECU opens the vacuum switching valve (VSV) to prevent EGR flow.

When coolant temperature exceeds the specified value, the ECU closes the VSV to allow EGR flow. The vacuum modulator opens at idle speeds to prevent EGR flow when coolant temperature exceeds the specified value.

ELECTRONIC CONTROLLED TRANSMISSION (ECT)

Automatic transmission models are equipped with an electronic control unit to control transmission operation. The ECU of the TCCS provides signals on engine operation to the ECU of the ECT system. This information is used by the ECT computer to prevent shift up to 3rd gear or overdrive during cold engine operation.

Note. The ECU of the TCCS is not interchangeable with the ECU of the ECT system.

DIAGNOSTIC SYSTEM

The ECU of the TCCS is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECU lights the "CHECK ENGINE" lamp located on instrument panel.

By analyzing various signals, the ECU detects system malfunctions which are related to various operating parameter sensors. The ECU stores failure codes associated with the detected failure until the diagnosis system is cleared. Clear the diagnosis system by removing the "STOP" fuse with ignition switch in "OFF" position.

A "CHECK ENGINE" warning light on instrument panel informs driver that a malfunction has been detected. The light goes out automatically when malfunction has been cleared.

CATALYTIC CONVERTER

All models are equipped with 3-way catalytic converters. This type of converter changes CO, HC, and NOx exhaust emissions into carbon dioxide, water vapor and nitrogen gas. The converter is a monolithic type.

DIAGNOSIS

Diagnose TCCS system in the following order

1. Ensure that all engine systems NOT related to TCCS are fully operational. Do not proceed with testing until all other problems have been fixed. Always check fuses, fusible links and wire connectors before condemning the ECU.
2. Enter diagnostic mode and record trouble codes. Exit diagnostic mode. If no trouble codes were displayed, go to «DIAGNOSTIC CIRCUIT CHECK»(/toyota/4runner/i-1984-1989/remont/testing-diagnostics/#tccs-system__diagnostic-circuit-check-scheme-66) chart. Follow instructions given there.
3. If no trouble codes were displayed after performing diagnostic circuit check, perform voltage and resistance checks. If trouble codes are displayed, perform tests to confirm cause of malfunction which set the corresponding trouble code.
4. After any repairs are made, clear trouble codes and perform diagnostic circuit check. Normal system operation code should be displayed if repair solved cause of malfunction.

Note. The following paragraphs explain the procedures involved in performing the steps outlined

RECALLING TROUBLE CODES

The ECU stores component failure information for the TCCS under a related trouble code which can be recalled for diagnosis and repair. A malfunction is indicated by the "Engine Light" blinking a number of times equal to the malfunction code indication, with a 2.5 second delay between each indication. (Scheme 65)

The diagnostic code series will be repeated as long as the "CHECK ENGINE" connector terminals T - E1 are shorted. In the event of a number of trouble codes, indication will begin from the smaller value and continue to the larger in order.

Scheme 63

1. Prior to entering diagnostic mode, the following conditions must be met. Engine must be at normal operating temperature, battery voltage above 11 volts, transmission in "P" or "NEUTRAL", throttle valve fully closed and A/C off.
2. Turn ignition switch to "ON" position. DO NOT start engine. Simultaneously push and hold in "SELECT" and "INPUT" "M" keys for at least 3 seconds. (Scheme 63) The letters "DIAG" will appear on screen. (Scheme 63): Super Monitor Display
3. After a short pause, hold in "SET" key for at least 3 seconds. If system is normal, "E/G OK" will appear on screen. If there is a malfunction, the code number for the malfunction will appear on the screen. In the event of 2 or more numbers, there will be a 3 seconds pause between each number.

Entering Diagnostic Mode Without Super Monitor Display

1. Prior to entering the diagnostic mode, the following conditions must be met. Engine must be at normal operating temperature, battery voltage above 11 volts, transmission in "P" or "NEUTRAL", throttle valve fully closed and A/C off.
2. Turn ignition on, but DO NOT start engine. Remove rubber cap from "CHECK ENGINE" connector. Using a jumper wire, jump terminals T - E1 of the connector together. (Scheme 64)

Jumping "CHECK ENGINE" Connector Insert jumper wire in "CHECK ENGINE" connector. Scheme 64

Diagnostic Code Output

1. To obtain an output of diagnostic codes, ensure battery voltage is above 11 volts, throttle valve is fully closed, transmission is in "P" or "NEUTRAL" positions, all accessory switches are in "OFF" position, and engine is at normal operating temperature.
2. Turn ignition switch to "ON" position. DO NOT start engine. Using a sub-wire, short terminals T - E1 of "CHECK ENGINE" connector. (Scheme 64)
3. Read diagnosis code as indicated by number of flashes of "CHECK ENGINE" warning light. (Scheme 65) Refer to «TCCS TROUBLE CODE IDENTIFICATION»(/toyota/4runner/i-1984-1989/remont/testing-diagnostics/#tccs-system) table for diagnosis codes.
4. The "CHECK ENGINE" warning light will blink a number of times equal to the malfunction code indication with a 2.5 second delay between each indication. The diagnostic code series will be repeated as long as "CHECK ENGINE" connector terminals T - E1 are shorted.

Note. In the event a number of trouble codes are to be identified, indication will begin from the smaller value and continue to the larger in order.

Example of Trouble Code Output. Scheme 65

Clearing Trouble Codes

After any repairs are performed, clear ECU memory of all stored trouble codes. To clear memory, turn ignition off and remove 15A "EFI" fuse from fuse panel for 30 seconds. The lower the ambient (outside) temperature, the longer the fuse must be left out. Replace fuse and exit diagnostic mode.

Exiting Diagnostic Mode

To exit diagnostic mode with Super Monitor Display, either switch or push the Super Monitor Display key to display time.

For diagnostic mode without Super Monitor Display, remove jumper wire from "CHECK ENGINE" connector. Turn ignition off. Replace rubber caps over connectors. After cancellation, perform a road test to confirm that a "NORMAL" code is now displayed.

TCCS Voltage Tests

The TCCS can be checked using a voltmeter. Before making voltage tests, make sure battery voltage is at least 11 volts. Perform voltage tests with harness connectors connected to ECU and ignition switch in "ON" position. Connect probes to each wire cavity of ECU connectors. If voltage values are not as specified, perform resistance tests.

TCCS Resistance Tests

The TCCS can be checked using an ohmmeter. Before making resistance tests, turn ignition off and disconnect wiring connectors at ECU. Insert ohmmeter probes into wiring connectors from wire side. Measure resistance at connector terminals, NOT at ECU terminals.

TCCS TROUBLE CODE IDENTIFICATION

TROUBLE CODES & PROBABLE CAUSE

Diagnostic Circuit Check. Scheme 66

Terminals No. 10 & No. 20 - E01. Scheme 67

Terminals VC - E2 & Vs - E2. Scheme 68

Terminal THW - E2. Scheme 69

Trouble Code 5, Oxygen Sensor (1 of 2). Scheme 70

Trouble Code 5, Oxygen Sensor (2 of 2). Scheme 71

Terminal IGt - E1. Scheme 72

Terminals IDL - E2. Scheme 73

Terminals VTA - E2 & Vcc - E2. Scheme 74

Terminals THA - E2. Scheme 75

TROUBLE CODE 9 VEHICLE SPEED SENSOR

Note. This code will set if the engine is revved over 3000 RPM. This is normal. There is no trouble shooting chart available for this code.

Terminal STA - E1. Scheme 76

Terminal +B/K - E1 & Terminal BAT - E1. Scheme 77

TROUBLE CODES 12-14

There are no Trouble Code Charts available from the manufacturer. See TCCS TROUBLE CODE IDENTIFICATION table and TROUBLE CODES & PROBABLE CAUSE table above for possible affected circuits and the probable cause.

Terminals W - E1. Scheme 78

Terminals B/K - E1. Scheme 79

Airflow Meter

Turn ignition off. Disconnect wiring connector from airflow meter. Using an ohmmeter, measure resistance between each terminal. (Scheme 80) If resistance values do not meet specifications shown in chart, replace airflow meter.

Measuring Airflow Meter Resistance. Scheme 80

AIRFLOW METER RESISTANCE SPECIFICATIONS

Scheme 81

1. After stopping engine, clicking sound should be heard from ISC valve. If not, remove ISC valve and perform operation check.
2. Drain engine coolant. Disconnect 2 electrical connectors, 2 coolant by-pass hoses and air hoses. Remove 2 bolts and ISC valve body.
3. Apply battery voltage to dual-terminal connector. Grounding terminals S1, S2, S and S4 in sequence should cause valve to close. (Scheme 81) With battery voltage still connected, grounding terminals in reverse sequence (S4, S, S2 and S1) should cause valve to open. If not, perform resistance check. (Scheme 81): Checking ISC Valve Operation Valve should open when voltage is applied in one direction and close when voltage is applied in reverse direction.
4. Check resistance values of ISC valve. Check resistance with ignition off and ISC electrical connector disconnected. If resistance is not as specified in chart, replace ISC valve.

ISC VALVE RESISTANCE SPECIFICATIONS

Turn ignition off and disconnect electrical connector at TPS. Insert a thickness gauge between throttle stop screw and throttle lever. Using an ohmmeter, check resistance values. (Scheme 82) If values are not as specified in chart, adjust or replace TPS.

Checking Throttle Position Sensor Perform adjustment before replacing. Scheme 82

TPS RESISTANCE SPECIFICATIONS

TCCS VOLTAGE & RESISTANCE TESTING

TCCS VOLTAGE & RESISTANCE SPECIFICATION CHART (1)

Scheme 83

1. Loosen 2 TPS retaining screws. Insert a thickness gauge between throttle stop screw and throttle. With ignition off and electrical connector disconnected, connect ohmmeter between terminals IDL and E1 or E2. (Scheme 82) THROTTLE POSITION SENSOR ADJUSTMENT Model Gap In. (mm) All Models.019 (.47) (Scheme 83): Adjusting Throttle Position Sensor
2. Gradually turn TPS counterclockwise until ohmmeter needle deflects. Secure TPS retaining screws. Using a thickness gauge, recheck the continuity between terminals IDL - E1 or E2.

TCCS Wiring Diagram. Scheme 84

See also:
• FUEL INJECTION SYSTEM - BOSCH AFC
• DIAGNOSTIC CIRCUIT CHECK
• TCCS TROUBLE CODE IDENTIFICATION