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Tach Pulse Signal

  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 proper ECU test harness terminals with engine cranking. See Fig 1 . See ECU TACH SIGNAL & RESISTANCE TEST TERMINALS table. If a pulsed signal is present, no fault is present. If pulsed signal is not present, check sensor and wiring integrity.
    Fig 1: Identifying ECU Test Harness Connector Terminals
    G91A16519Courtesy of AMERICAN HONDA MOTOR CO., INC.
  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  table. 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. See Fig 2 or Fig 3 .
  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.
  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 2 -Fig 3 and SENSOR RESISTANCE TEST TERMINALS  table. If continuity to ground exists, replace sensor.
    ECU TACH SIGNAL & RESISTANCE TEST TERMINALS

    Application Terminals Ohms
    Prelude 2.0L
    CRANK B10 & B12 700-1000
    CYL C1 & C2 700-1100
    TDC C3 & C4 700-1000
    Prelude 2.1L
    CRANK B15 & B16 700-1000
    CYL B11 & B12 700-1100
    TDC B13 & B14 700-1000
    Fig 2: Prelude TDC/CRANK Sensor Connector Terminal ID
    G94641Courtesy of AMERICAN HONDA MOTOR CO., INC.
    Fig 3: Prelude CYL Sensor Connector Terminal ID
    G94642Courtesy of AMERICAN HONDA MOTOR CO., INC.
    SENSOR RESISTANCE TEST TERMINALS

    Application Terminal or Wire Color
    Prelude
    CRANK C & D
    CYL Orange & White
    TDC A & B
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