I-Tec Control System Isuzu Impulse I

DESCRIPTION

The I-TEC control system constantly monitors and controls engine operation. This lowers emissions while maintaining fuel economy and driveability. The Electronic Control Unit (ECU) controls the fuel injection system, the ignition system, and the turbocharger control system (if used).

The fuel injection system consist of the crank angle sensor, the throttle valve switch, the vehicle speed sensor, the coolant temperature sensor, the air flow sensor, the oxygen sensor, 4 fuel injectors, and the ECU.

The ignition system consist of the crank angle sensor, the throttle valve switch, the vehicle speed sensor, the coolant temperature sensor, the air flow sensor, the knock sensor, a transistorized ignition coil, and the ECU.

The turbocharger control system consist of the throttle valve switch, the throttle position sensor, the knock sensor, the coolant temperature sensor, the air flow sensor, the oxygen sensor, the stepping motor, the turbocharger controller, and the ECU.

DATA SENSORS

The sensors provide electrical impulses to ECU by monitoring vacuum, temperature, pressure, and other engine operating conditions. Location and operation of each sensor is as follows

Air Flow Sensor

The air flow sensor is located in the air cleaner housing. The air flow sensor measures the rate (volume) of air intake.

Oxygen Sensor

The sensor is threaded into the exhaust manifold. The oxygen sensor measures and produces an electrical signal proportional to the amount of oxygen present in the exhaust gases.

Crank Angle Sensor

This sensor is located inside the distributor housing. The engine speed and relative position of each piston in its cylinder are detected. From these parameters, ECU calculates proper ignition timing and dwell angle. The ECU then sends a signal to the transistorized ignition coil, to create a spark.

Knock Sensor

The knock sensor is located on the cylinder head. The sensor sends electrical impulses to the ECU when "knocking" occurs. The ECU retards timing to reduce detonation.

Coolant Temperature Sensor

This sensor is located on the engine block, under the intake manifold. It sends coolant temperature information to ECU. This information is used by ECU to determine engine temperature for calculating required air/fuel mixture.

Throttle Valve Switch

The throttle position switch is located on the throttle body. It detects throttle valve position at engine idle, part throttle, and wide open throttle.

Throttle Position Sensor

The throttle position sensor is used in turbocharged engines only. The sensor controls the fuel cut system.

Vehicle Speed Sensor

The sensor is built into the speedometer. The ECU receives electrical impulses from the vehicle speed sensor.

ELECTRONIC CONTROL UNIT (ECU)

The ECU is located under the instrument panel. The ECU analyzes all electrical data signals from the sensors. It controls the fuel injection system, the ignition system, and the turbocharger control system (if used). The ECU has built in back-up, diagnostic, and fail-safe control systems.

BACK-UP CONTROL SYSTEM

In the event of a malfunction has developed in the micro-computer within the electronic control unit, the back-up control system works to maintain the necessary functions of the control unit to permit continuous operation of the vehicle.

DIAGNOSTIC SYSTEM

The ECU is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECU will store a code in its memory. ECU will also turn on a "CHECK ENGINE" lamp located on the instrument panel.

As a bulb and system check, the "CHECK ENGINE" lamp will glow when ignition switch is on and engine is not running. When engine is started, the lamp should go out after 4 seconds. If not, a malfunction has been detected in the I-TEC system.

Note. The ECU self-diagnosis system is capable of troubleshooting the electrical circuits in the I-TEC system only. The ECU can not detect problems in the data sensors, secondary ignition, fuel injection system or engine mechanical conditions.

FAIL-SAFE SYSTEM

If a failure takes place in the oxygen sensor, coolant temperature sensor circuit, throttle valve switch, air flow sensor, or the knock sensor circuit. The output of the electronic control unit will switched automatically to the fail-safe mode.

FUEL CUT SYSTEM

See FUEL INJECTION SYSTEM - ISUZU I-TEC article in FUEL INJECTION section.

PRELIMINARY INSPECTION

Perform the following inspection before diagnosing the I-TEC control system. Ensure all engine systems NOT related to the system are fully operational. DO NOT proceed with testing unless all problems have been corrected. Repair or replace parts as necessary.

Handling Precautions

1. DO NOT get water on I-TEC system. Pay particular attention to the relay box and throttle valve switch. This connector is not water-proofed and will be adversely affected by water.
2. A 12 volt battery should always be used. When charging the battery without removing it from the vehicle, the battery cable MUST be disconnected. NEVER disconnect the battery cable when the engine is running, the voltage surge created may damage the electronic control unit or other system components.
3. When checking or replacing parts of the I-TEC system, ensure that the ignition switch is in the "OFF" position. When measuring voltage at the electronic control unit harness connector, disconnect all of the control unit harnesses first, then place the ignition switch to the "ON" position.
4. When checking the electrical terminals of the ECU with a tester, DO NOT apply probe directly to terminal. Insert a pin into terminal from harness side, and perform the measurement through pin. If the probe is held against terminal, the terminal will become distorted, causing a poor connection.
5. DO NOT pry or tap on I-TEC system components. I-TEC components and connectors are very sensitive to shock, distortion and water. A slight distortion or dent will seriously affect performance.

Fuel System

See PRELIMINARY INSPECTION in the article FUEL INJECTION SYSTEM - ISUZU I-TEC in FUEL SYSTEMS section.

Air Intake System

1. Ensure no air is drawn in from air duct and connecting hose joints. Make sure no air is drawn in at the intake manifold. Make sure no air is drawn in at the EGR valve.
2. Ensure that vacuum hoses at brake booster, EGR, pressure regulator, and fuel evaporation canister are correctly installed, not damaged, or collapsed. On turbo models, check vacuum hose connections at air switching valve, cruise control actuator vacuum tank, and at boost gauge.
3. On all models, check that PCV hose is connected properly, not damaged, or collapsed. Make sure that oil filler cap is installed correctly. Ensure that oil level gauge is installed correctly.

Electrical System

Ensure that all electrical harnesses for the I-TEC system are connected properly. Make sure that connecting terminals and connectors are free from corrosion and in good condition. All I-TEC wires must be at least 4" (100 mm) from any high tension cables.

DIAGNOSTIC PROCEDURE

The ECU stores circuit failure information under a related trouble code which can be recalled for diagnosis and repair. When recalled, these codes will be displayed by flashes of the "CHECK ENGINE" lamp. Codes start with lowest numbered code. Only codes in which a related malfunction has occurred will be displayed.

Note. An example of trouble codes is as follows: "FLASH", "FLASH", pause, "FLASH", "FLASH", "FLASH" followed by a longer pause identifies trouble code 23. First series of flashes indicates first digit of trouble code. Second series of flashes indicates second digit of trouble code.

Entering Diagnostic Mode

1. Turn ignition on. "CHECK ENGINE" lamp should light. Locate diagnostic leads. (Scheme 9) Connect diagnostic terminal leads together. If any trouble codes are stored in ECU memory, the "CHECK ENGINE" lamp will flash 2-digit codes.
2. The trouble codes will be displayed from lowest to highest numbered code. Each code is repeated three times before the next code sequence is displayed. The trouble codes will be repeated as long as the diagnostic terminals are connected and the ignition is on.

I-TEC Diagnostic Leads & Fuse Location Remove fuse No. 4 to clear memory. Scheme 9

ECU TROUBLE CODE IDENTIFICATION

Impulse I-TEC System Wiring Diagram. Scheme 10

Clearing Trouble Codes

After completion of service, clear memory of trouble codes, by removing fuse No. 4 in fuse box. (Scheme 9) Make sure that only code 12 is displayed. Disconnect diagnostic terminals.

Note. Disconnecting the 13 pole connector from the ECU will also clear the memory. Removing fuse No. 4 will also stop clock and other electrical equipment. Reset clock.

DIAGNOSTIC TOOLS

The I-TEC system does not require special tools for diagnosis. An ohmmeter, a voltmeter, 2 jumper wires 6" (40 cm) long, a 1.5 volt battery, a jumper wire 10 ft. (3 meters) long fitted at ends with a pin and an alligator clip.

CIRCUIT INSPECTION

The control unit harnesses are connected with 3 types of connectors, each of which has specific numbers. Inspection procedures will be described with reference made to specific numbers. When checking the system, carefully note the terminal number to avoid a direct battery connection when ignition switch is turned on.

1. The inspection based on the trouble codes should be performed in the following steps: Check continuity of sensor(s). Check continuity of sensor circuit(s). Check electronic control module.
2. Disconnect wiring at ECU, sensor or output device when testing for shorts or continuity. When checking control unit harness connector terminals, make connection by inserting a pin into terminal from harness side. Avoid connecting tester probe directly to control unit terminal.
3. If trouble is not found in sensor(s) or in circuit(s), clear the memory and reconnect circuit(s). Road test vehicle. Obtain code display to see if trouble has been corrected. If trouble persists, replace the control unit.

ECU Connector Terminal Identification. Scheme 11

TEST 1 - POWER SUPPLY CHECK

1. Unplug ECU connectors at ECU. Turn ignition on, and check for battery voltage at ECU connector terminal No. 29 and 41. If battery voltage is present, go to step 2). If no voltage at terminals, check main relay, ignition switch, fuses, fusible links, and circuits.
2. Check for continuity between ECU connector terminal No. 38, No. 39, and ground. If ohmmeter does not show continuity to ground, check ground connection, terminal ends, and wires.

Power Supply Check. Scheme 12

Circuit Testing

Unplug ECU connectors at ECU. Disconnect oxygen sensor lead at connector. Check for continuity and between ECU connector terminal No. 30 and oxygen sensor connector. If no continuity exists, repair or replace harness. 2 If circuit is good, install a new oxygen sensor. Road test vehicle. Check if same trouble code is displayed.

Sensor Testing

Note. A voltmeter with an internal resistance of at least 20,000 ohms must be used to check the oxygen sensor.

1. Disconnect oxygen sensor lead at connector. Insert a thin test wire into connector so that wire is exposed. Reconnect oxygen sensor lead. Set tester on 2 volt scale.
2. Connect positive lead of tester to test wire and negative lead to ground. Start engine, and check for voltage variations between 0 and 0.8 volts when engine speed is momentarily increased. Replace oxygen sensor if no voltage variation is noted.

Oxygen Sensor Connector. Scheme 13

Measure the resistance across the coolant temperature sensor terminals. Compare sensor resistance to coolant temperature. Replace coolant temperature sensor if resistance does not meet specifications.

TESTING COOLANT TEMPERATURE SENSOR

Reconnect harness to coolant temperature sensor. Unplug ECU connectors at ECU. Check continuity of circuit as indicated in table. If readings are incorrect, repair or replace harness.

TESTING COOLANT TEMPERATURE SENSOR CIRCUIT

Water Temperature Sensor. Scheme 14

TEST 4 - THROTTLE VALVE SWITCH (CODES 21, 43 AND 65)

1. Check throttle valve switch See the article «FUEL INJECTION SYSTEM - ISUZU I-TEC»(/isuzu/impulse/i-1983-1990/remont/testing-diagnostics/#fuel-injection-system-isuzu-i-tec) in FUEL INJECTION section. If throttle switch is okay, and code 21 or 43 is displayed, go to step 2). If throttle switch is okay, and code 21 or 65 is displayed, go to step 3).
2. Connect an ohmmeter between ECU connector terminal No. 2 and Green/Red wire. Ohmmeter reading should be infinity. If reading is incorrect, repair or replace harness.
3. Connect an ohmmeter between ECU connector terminal No. 13 and Blue/Yellow wire. Ohmmeter reading should be infinity. If reading is incorrect, repair or replace harness.

Throttle Valve Switch. Scheme 15

TEST 5 - STARTER SIGNAL (CODE 22)

Unplug ECU connectors at ECU. Disconnect ignition switch harness at switch. Check continuity between terminal 4 of ignition switch and ECU connector terminal No. 25. If no continuity exists, repair or replace harness.

Starter Signal. Scheme 16

TEST 6 - CRANK ANGLE SENSOR (CODE 41)

1. Remove relay box cover. Disconnect crank angle sensor at connector. Connect an ohmmeter between terminals 12 and W. Ohmmeter reading should be 0 ohms. Connect an ohmmeter between terminals 1 and G. Ohmmeter reading should be 0 ohms. If readings are incorrect, repair or replace harness.
2. Connect a voltmeter between terminal 12 and ground. Voltage reading should be 10-14 volts. Connect an ohmmeter between terminal B and ground. Ohmmeter reading should be 0 ohms. If circuits are good, replace distributor assembly.

Crank Angle Sensor. Scheme 17

1. Partly raise sealing gasket on air flow sensor side of harness connector. Connect an ohmmeter between Black wire and ground. Ohmmeter reading should be 0 ohms. Check voltage across sensor wires and ground as indicated in table. TESTING AIR FLOW SENSOR Wire Color Condition Volts Red Ignition On 10-14 Green Ignition On 0.2-0.6 Green Engine Running 1.0-2.0
2. If readings in Red and Black wires are incorrect, check air flow sensor circuit and repair as necessary. If readings in Red and Black wires are correct, but voltage in Green wire is incorrect, replace air flow sensor.

Unplug ECU connectors at ECU. Disconnect air flow sensor harness at sensor. Check air flow sensor circuit continuity as indicated in table. If readings are incorrect, repair or replace harness.

TESTING AIR FLOW SENSOR CIRCUIT

Air Flow Sensor Connector. Scheme 18

TEST 8 - VEHICLE SPEED SENSOR (CODE 63)

1. Unplug ECU connectors at ECU. Connect ohmmeter between ECU connector terminal No. 5 and ground. Disconnect speedometer cable from transmission and turn inner cable slowly.
2. If vehicle speed sensor circuit is good, ohmmeter will show open and closed circuit alternately. If no signal pulses are found, remove instrument cluster.
3. Connect ohmmeter across connector terminals on back of instrument cluster. Using a screwdriver, slowly turn speedometer. If sensor is defective, replace speedometer assembly. If sensor is good, ohmmeter will show open and closed circuit alternately.
4. Check continuity between Yellow wire and ECU connector terminal No. 5. Ohmmeter reading should be 0 ohms. Check continuity between Yellow wire and ground. Ohmmeter reading should be infinity. If readings are incorrect, repair or replace harness.

Vehicle Speed Sensor (Code 63). Scheme 19

TEST 9 - DETONATION SENSOR (CODE 66)

1. Unplug ECU connectors at ECU, and at knock sensor. Check resistance across sensor. Resistance should be 650-800 ohms. Replace sensor if reading is different.
2. If reading is okay, check continuity of circuit as indicated in table. If readings are incorrect, repair or replace harness.

TESTING KNOCK SENSOR CIRCUIT

TEST 10 - MCU (CODES 51, 52 AND 55)

Unplug ECU connectors and check all terminals. Reconnect ECU connectors and road test vehicle. Check to see if trouble codes have been corrected. If trouble codes are still present, replace ECU.

TEST 11 - POWER TRANSISTOR SYSTEM (CODES 23, 35 AND 54)

1. Disconnect power transistor harnesses at connector. Disconnect high tension wire between coil and distributor cap. Hold high tension lead 1/4" (6 mm) away from ground. Turn ignition switch on.
2. Use a jumper wire to connect "Y" terminal of transistor to positive side of 1.5 volt battery. Connect negative side of battery to ground. Disconnect jumper wire from battery. Check to see if a spark is created from the high tension lead to ground. If a spark is not created, replace power transistor and bracket assembly.
3. If transistor is okay, unplug ECU connectors at ECU. Disconnect wire from ignition coil. Check continuity of transistor circuit as indicated in table. If readings are incorrect, repair or replace harness.

TESTING POWER TRANSISTOR CIRCUIT

Power Transistor System (Codes 23, 35 & 54). Scheme 20

TEST 12 - VACUUM SWITCHING VALVE (CODE 25 AND 53)

1. Check vacuum switching valve. See the «FUEL INJECTION SYSTEM - ISUZU I-TEC»(/isuzu/impulse/i-1983-1990/remont/testing-diagnostics/#fuel-injection-system-isuzu-i-tec) article in the FUEL SYSTEMS section. Unplug ECU connectors at ECU, and at vacuum switching valve. If trouble code 25 is present, go to step 2). If trouble 53 is present go to step 4).
2. Turn ignition switch on. Connect a voltmeter between vacuum switching valve Black/White feed wire and ground. Voltage reading should be 12 volts. Turn ignition switch off. If reading is incorrect, repair or replace harness.
3. Connect an ohmmeter between vacuum switching valve Lt. Green/Yellow feed wire and ECU connector terminal No. 35. Ohmmeter reading should be 0 ohms. If reading is incorrect, repair or replace harness.
4. Connect an ohmmeter between ECU connector terminal No. 23 and ground. Ohmmeter reading should be 0 ohms. Connect an ohmmeter between ECU connector terminal No. 33 and ground. Ohmmeter reading should be 0 ohms. If readings are incorrect, repair or replace harness.

Vacuum Switching Valve. Scheme 21

TEST 13 - FUEL INJECTOR CIRCUITS (CODE 33)

1. Turn ignition switch on. Check that voltage is being applied to ECU connector terminal No. 21 and 22. If voltage is not present, disconnect fuel injector harnesses at connector.
2. Check that voltage is present at connectors. If voltage is not present, check dropping resistor, main relay and ignition switch. Turn ignition switch off.
3. Check continuity of injector circuit as indicated in table. If readings are incorrect, repair or replace faulty parts.

TESTING FUEL INJECTOR CIRCUIT

Note. If ECU connector terminal No. 21 is shorted, also check multi-drive monitor for short to ground.

Fuel Injector Circuits (Code 33). Scheme 22

TEST 14 - INJECTOR TRANSISTOR GROUND CIRCUIT (CODE 64)

Unplug ECU connectors at ECU. Connect an ohmmeter between ECU connector terminal No. 31 and ground. Ohmmeter reading should be 0 ohms. Connect an ohmmeter between ECU connector terminal No. 32 and ground. Ohmmeter reading should be 0 ohms. If readings are incorrect, repair or replace faulty parts.

Impulse (I-TEC) Emission Control Diagram (Turbo). Scheme 23

Impulse (I-TEC) Emission Control Diagram (Except Turbo). Scheme 24

See also:
• FUEL INJECTION SYSTEM - ISUZU I-TEC