1990 Honda Civic Base, 2D HatchbackFACTORY OEM SERVICE PROCEDURE

Tach Pulse Signal (Fuel Injected)

  1. Timing control and triggering of fuel injectors are based upon input signals from TDC/CRANK/CYL sensors. See TIMING CONTROL SENSOR USAGE  table. These sensors are simple PM (Permanent Magnet) generator pick-up coils.
  2. Using a DVOM on low voltage scale (preferably with a bar-graph function), check for a pulsed low-voltage signal at the proper ECU harness terminals with engine cranking. See ECU TACH SIGNAL & RESISTANCE TEST TERMINALS  . If a pulsed signal is present, no fault is present. If pulsed signal is not present, check sensor and wiring integrity.
  3. To test sensor and wiring integrity, turn ignition off. Disconnect connectors from ECU. Lightly probe appropriate ECU harness terminals to check for proper winding resistance of each sensor. See ECU TACH SIGNAL & RESISTANCE TEST TERMINALS  . If resistance is within specification, go to step 5). If resistance is not within specification, check resistance of TDC/CRANK/CYL sensor (if equipped) directly at sensor connector.
  4. If sensor resistance is now within specification, repair opens, shorts or corrosion in wire harness between sensor(s) and ECU. If resistance is not within specification, replace sensor/distributor assembly.
  5. If resistance values in step 3) were within specification, check for continuity to ground at each ECU sensor terminal. If continuity is present, disconnect sensor(s) and recheck for continuity to ground at ECU sensor terminals. If continuity no longer exists, go to the next step. If continuity to ground is still present, repair short to ground in ECU harness between ECU and sensor(s).
  6. If continuity did not exist with sensor disconnected, check for continuity to ground on each sensor connector. See Fig 1 and Fig 2 and SENSOR RESISTANCE TEST TERMINALS  table. If continuity to ground exists, replace sensor/distributor assembly.
    ECU TACH SIGNAL & RESISTANCE TEST TERMINALS

    Application Terminals Resistance (Ohms)
    Civic 1.5L & CRX Std. (TBI)
    CRANK C1 & C2 350-550
    TDC C3 & C4 350-550
    Civic 1.6L, CRX HF & CRX Si (PFI)
    CRANK B10 & B12 350-550
    CYL C1 & C2 350-550
    TDC C3 & C4 350-550
    Fig 1: 1.5L & CRX Std. TBI TDC/CRANK Sensor Connector Terminals
    G90H04370Courtesy of AMERICAN HONDA MOTOR CO., INC.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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