STEP GP 3844089 - Caterpillar

Illustration 2 g00668980
J1/P1 breakout
Measure the voltage between P1:29 (Digital Return) and P1:32 (+V Timing) at the breakout.
Turn the keyswitch to the OFF/RESET position.Expected Result:The voltage is 12.5 1.0 VDC.Results:
OK - There is an open circuit or excessive resistance in the harness between the ECM and the sensor.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOP
Not OK - Repair: Ensure that the ECM is receiving the correct supply voltage. Refer to Troubleshooting, "Electrical Power Supply Circuit - Test". If the ECM is receiving the correct supply voltage, proceed to Test Step 8.Test Step 8. Check for a Short Circuit in the Wiring Harness
Turn the keyswitch to the OFF/RESET position.
Disconnect ECM connector J1/P1 and the suspect connector for the engine speed/timing sensor.
Measure the following resistances at the suspect engine speed/timing sensor (harness side).
Terminal A (+V Timing) and Terminal B (Digital Return)
Terminal A (+V Timing) and Terminal C (Signal)
Terminal B (Digital Return) and Terminal C (Signal)
Terminal A (+V Timing) and engine ground
Terminal B (Digital Return) and engine ground
Terminal C (Signal) and engine groundExpected Result:The resistance is greater than 20,000 Ohms for each measurement.Results:
OK - Proceed to Test Step 9.
Not OK - There is a short circuit in the harness or connectors.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 9. Check the Resistance through the Harness
Illustration 3 g00668980
ECM connector P1 (ECM side)
Fabricate a jumper wire with pins at both ends.
Use the jumper wire to short P1:32 (+V Timing) and P1:29 (Digital Return) together.
Measure the resistance between J20:A (+V Timing) and J20:B (Digital Return).
Measure the resistance between J44:A (+V Timing) and J44:B (Digital Return).
Use the jumper wire to short P1:32 (+V Timing) and P1:38 (Primary Speed/Timing).
Measure the resistance between J20:A (+V Timing) and J20:C (Primary Speed/Timing).
Use the jumper wire to short P1:32 (+V Timing) and P1:39 (Secondary Speed/Timing).
Measure the resistance between J44:A (+V Timing) and J44:C (Secondary Speed/Timing).
Remove the jumper wire and reconnect all of the connectors.Expected Result:The resistance is less than 10 Ohms when the jumper wire is installed.Results:
OK - The harness resistance is within acceptable limits. Proceed to Test Step 10.
Not OK - There is an open circuit or excessive resistance in the harness or connectors.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 10. Check the Signal Voltage at the ECM
Turn the keyswitch to the ON position.
Illustration 4 g00668980
J1/P1 breakout
Measure the signal voltage at the breakout, as follows:Primary Engine Speed/Timing SensorMeasure the voltage between P1:38 (Primary Speed/Timing) and P1:29 (Digital Return) at the breakout. Perform this step with the keyswitch in the ON position before you crank the engine and while you crank the engine.Secondary Engine Speed/Timing SensorMeasure the voltage between P1:39 (Secondary Speed/Timing) and P1:29 (Digital Return) at the breakout. Perform this step with the keyswitch in the ON position before you crank the engine and while you crank the engine.
Turn the keyswitch to the OFF position.Expected Result:The voltage is less than 3.0 VDC or the voltage is greater than 10.0 VDC with the keyswitch in the ON position. The voltage varies between 2.0 VDC