Tach Pulse Signal (Fuel Injected)

Timing control and triggering of fuel injectors are based upon input signals from the TDC, CRANK, and CYL sensors. These sensors are simple PM (Permanent Magnet) generator pick-up coils.

1. Test for a pulsed tach signal. Using a DVOM on the low-volts scale (preferrably 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 exists, no fault is present. If pulsed signal is not present, check sensor and wiring integrity.
   ECU TACH SIGNAL & RESISTANCE TEST TERMINALS
   
   

   Application		Terminals	Resistance (Ohms)
   Civic 1.5L & CRX Std.
   CRANK		C1 & C2	350-550
   TDC		C3 & C4	350-550
   Civic 1.6L & CRX HF & Si
   CRANK		B10 & B12	350-550
   CYL		C1 & C2	350-550
   TDC		C3 & C4	350-550

2. 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 4). If resistance is not within specification, check resistance of CRANK, CYL and TDC sensor (if equipped) directly at sensor connector. See Fig 1 and Fig 2 .
3. If sensor resistances are now within specification, repair opens, shorts or corrosion in wire harness between sensor(s) and ECU. If resistances are not within specification, replace sensor/distributor assembly.
4. If resistance values in step 2). were within specification, check for continuity to ground at each ECU sensor terminal. If continuity exists, 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 still exists, repair short to ground in ECU harness between ECU and sensor(s).
5. 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.
   Fig 1: Civic 1.5L & CRX Std. Fuel Injected CRANK/TDC Sensor Connector Identification

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
   Fig 2: Civic 1.6L & CRX HF & Si Fuel Injected CRANK/CYL/TDC Sensor Connector Identification

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
   SENSOR RESISTANCE TEST TERMINALS
   
   

   Application		Terminal or Wire Color
   Civic 1.5L & CRX Std.
   CRANK		D & E
   TDC		B & C
   Civic 1.6L & CRX HF & Si
   CRANK		C & D
   CYL		F & G
   TDC		A & B