LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Isuzu >> 1983 >> Impulse Automatic >> Repair and Diagnosis >> Engine Performance >> System >> I-TEC Control System >> Operation >> Diagnostic System
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic System

The MCU is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the MCU will store a code in its memory. MCU 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 MCU self-diagnosis system is capable of troubleshooting the electrical circuits in the I-TEC system only. The MCU can not detect problems in the data sensors, secondary ignition system, fuel delivery system or engine mechanical conditions.

Diagnosis of the I-TEC system is done in the following order:

  1. Ensure all engine systems NOT related to the system are fully operational. DO NOT  proceed with testing unless all other problems have been corrected. Ensure that all electrical and vacuum connections are correct and in good condition. All I-TEC wires must be at least 4" (100 mm) from any high voltage cables.
  2. Ensure all fuel hoses are tight and in good order. Check fuel pump operation. Pressure should be 36 psi (2.5 kg/cm2 ) when vacuum hose is disconnected from the pressure regulator. Be sure there is no water in fuel tank or any other part of system.
  3. Check fuel injection system for proper operation and leakage. Measure the resistance of the dropping resistor. Inspect air regulator electrical connection, cold idle speed and hoses. Check and adjust throttle position switch. See appropriate fuel injection article in FUEL INJECTION SYSTEM - I-TEC EFI article in the FUEL SYSTEMS section.
  4. Check and adjust idle speed and ignition timing. See appropriate Tune-Up Service article in TUNE-UP - 4-CYL in the ENGINE PERFORMANCE section.
  5. Display trouble codes in the MCU memory. To do this, follow procedure given for Entering Diagnostic Mode. The MCU will "FLASH" the trouble codes in the "CHECK ENGINE" lamp.
  6. If trouble codes were displayed, go to Diagnostic Circuit Check chart. Follow instructions given in chart.
  7. After any MCU circuit repairs are made, clear any trouble codes. Road test vehicle, making sure "CHECK ENGINE" lamp remains off.
Fig 1: Impulse I-TEC Diagnostic Leads Location
G42065
scientia non olet · About LEMON Manuals