LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Honda >> 1990 >> Civic Si >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - EFI >> Computerized Engine Controls >> Control Unit >> Power Circuits
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Power Circuits

  1. Using a voltmeter, check for battery voltage between ECU power terminal and ground. See POWER & GROUND TERMINAL IDENTIFICATION  table. See Figure and Figure . If battery voltage is not present, check appropriate ECU fuse in underhood fuse box. See ECU POWER CIRCUITS FUSE IDENTIFICATION  table. If fuse is okay, check for an open in wire between underhood fuse box and appropriate ECU power circuit terminal.
  2. Turn ignition switch to ON position. Using a voltmeter, check for battery voltage between appropriate ECU power circuit terminal and ground. See POWER & GROUND TERMINAL IDENTIFICATION  table. See Figure and Figure . If battery voltage is not present, check appropriate fuse in underhood fuse box. See ECU POWER CIRCUITS FUSE IDENTIFICATION  table. If fuse is okay, check for an open in wire between fuse box and appropriate ECU power circuit terminal, or check for a defective ignition switch.
    POWER & GROUND TERMINAL IDENTIFICATION

    Application (1) ECU Terminal
    Accord
    Ground Circuits A23, A24, A26 & B2
    Power Circuits
    Ignition Switch In OFF Position D1
    Ignition Switch In ON Position A25 & B1
    Civic & CRX
    Ground Circuits A2, A4, A16 & A18
    Power Circuits
    Ignition Switch In OFF Position B1
    Ignition Switch In ON Position A13 & A15
    Prelude
    2.0L
    Ground Circuits A2, A4, A16 & A18
    Power Circuits
    Ignition Switch In OFF Position A17
    Ignition Switch In ON Position A13 & A15
    2.1L
    Ground Circuits A23, A24, A26 & B2
    Power Circuits
    Ignition Switch In OFF Position D1
    Ignition Switch In ON Position A25 & B1
    (1) See Figure and Figure for terminal location identification.
    ECU POWER CIRCUITS FUSE IDENTIFICATION

    Application (1) Fuse
    Accord
    Ignition Switch In OFF Position Back-Up
    Ignition Switch In ON Position ECU
    Civic & CRX
    Ignition Switch In OFF Position Hazard
    Ignition Switch In ON Position ECU
    Prelude
    Ignition Switch In OFF Position Clock
    Ignition Switch In ON Position EFI/ECU
    (1) All fuses in underhood fuse box.