The Low RPM Indicator alerts the operator that the engine speed has decreased and the breaker needs to be tripped. When the engine reaches a predetermined point (1620 rpm) and the speed then decreases to 1600 rpm, a set of contacts inside the engine instrument panel will close activating a "Low RPM" signal.
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| Illustration 1 | g00852395 |
Test Step 1. Check for Connector Damage.
- Disconnect main power.
- 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 - The connectors and wiring are not free of problems.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 2. Check the Indicator.
- Start the engine.
- Shut down the engine.
- Observe the Low RPM Indicator on the Caterpillar Electronic Technician (ET).
Expected Result:
The indicator should activate when the engine shuts down.
Results:
- OK - The indicator activates when the engine shuts down.
Repair: The indicator is OK.
Stop.
- Not OK - The indicator does not activate when the engine shuts down. Proceed to test step 3.
Test Step 3. Check the Circuit.
- Close the switch to the +Battery terminal.
- Listen for the relay to change.
Expected Result:
The relay should activate and the lamp should illuminate.
Results:
- OK - The relay activated and the lamp illuminated. Proceed to test step 4.
- Lamp Illuminated - The relay did not activate but the lamp illuminated.
Repair: The problem appears to be with the relay. Temporarily install a new relay. If the problem is no longer present, reinstall the old relay. If the problem returns with the old relay, replace the relay.
Stop.
- Lamp Did Not Illuminate - The relay did not activate and the lamp did not illuminate.
Repair: The problem appears to be in the wiring between J2/P2 and the relay. Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 4. Check the Electronic Control Module (ECM).
- Disconnect the main power.
- Disconnect J1/P1 and J2/P2.
- Insert signal reading probes into P1-5 and P1-4.
- Connect the voltage test lamp to the signal reading probes.
- The voltage test lamp should illuminate. If the lamp does not illuminate, the lamp is faulty and/or there is a problem with the wiring. Continue this procedure until the lamp illuminates.
- Insert one signal reading probe into P1-5. Insert the other signal reading probe into P1-34.
- Connect the voltage test lamp to the signal reading probes.
- Connect an electronic service tool. Access the override. Enable the override for the Low RPM Relay.
- Disable the override.
Expected Result:
The voltage test lamp should illuminate when the override is enabled.
Results:
- OK - The voltage test lamp illuminates.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
- Not OK - The voltage test lamp did not illuminate. The problem is in the wiring between the Electronic Control Module (ECM) and the relay.
Repair: Replace the ECM. Perform the diagnostic procedure Troubleshooting, "Replacing the ECM".
Stop.