The sensor is used to calibrate the signal from the Speed/Timing Sensor. The sensor eliminates any mechanical errors.
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| Illustration 1 | g00928289 |
Test Step 1. Check for Connector Damage
- Turn the Engine Control Switch (ECS) to the OFF/RESET position.
- Check the connectors and wiring for the following problems: damage, corrosion, abrasion and incorrect attachment.
Expected Result:
The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.
Results:
- OK - The connectors and wiring are free of problems. Proceed to test step 2.
- Not OK -
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 2. Check for a Short Circuit and/or an Open Circuit.
- Disconnect J26/P26 and J1/P1.
- Measure the resistance between J26-1 and J26-2 .
Expected Result:
The resistance should be between 110 to 200 Ohms.
Results:
- OK - The resistance is between 110 to 200 Ohms. Proceed to test step 3.
- Not OK - The resistance is not between 110 to 200 Ohms. The sensor is internally shorted or open.
Repair: Replace the sensor.
Stop.
Test Step 3. Check for a Short Circuit in the Wiring Harness.
- Measure the resistance from J26-1 and J26-2.
- Measure the resistance from P26-1 to engine ground.
- Measure the resistance from P26-2 to engine ground.
Expected Result:
The resistance should be greater than 20,000 Ohms for each measurement.
Results:
- OK - The resistance is greater than 20,000 Ohms for each measurement. Proceed to test step 4.
- Not OK - The resistance is less than 20,000 Ohms indicating a short circuit.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 4. Check the Resistance Through the Harness.
- Use a suitable piece of wire and connect P26-1 to P26-2.
- Measure the resistance from P1-18 to P1-12.
Expected Result:
The resistance should be less than 10 Ohms through the wires.
Results:
- OK - The resistance is less than 10 Ohms through the wires. The Electronic Control Module (ECM) is not reading the sensor correctly. Proceed to test step 5.
- Not OK - The resistance is not less than 10 Ohms through the wires. There is an open circuit in the harness or connectors.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 5. Check the Signal Voltage at the Sensor Connectors.
- Reconnect all connectors.
- Turn the ECS to the BLACK START ENABLE position. Push the BLACK START ENABLE push button. The engine should be running.
- Accelerate the engine to low idle.
- Set a multimeter on the 20 VAC position.
- Measure the voltage between P1-18 and P1-12.
Expected Result:
The signal voltage should be greater than 6.0 VAC.
Results:
- OK - A valid signal voltage appears at the ECM connector P1. Proceed to test step 6.
- Not OK - The signal voltage is less than 6.0 VAC. There is a problem in the harness or the sensor.
Repair: Recheck for shorts or opens in the harness. If the problem is not resolved, adjust the air gap to approximately 0.9 mm (0.04 inch) and repeat this test.
Stop.
Test Step 6. Check for Diagnostic Codes.
- Turn the ECS to the OFF/RESET position.
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the ECS to the STOP position. The engine should be OFF.
- Check for ACTIVE diagnostic codes.
Expected Result:
The diagnostic code 277-08 should NOT be active.
Results:
- OK - The diagnostic code 277-08 is NOT active.
Repair: The sensor is working properly.
Stop.
- Not OK - A valid signal voltage appears at P1. The ECM is not reading the voltage properly.
Repair: Replace the ECM. Perform the diagnostic procedure Troubleshooting, "Replacing the ECM.".
Stop.