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Low System Voltage on Caterpillar ET Software

Low System Voltage

Figure 1.1 - Low Volt. Warning (Line Voltage)

#Voltage
The ECM automatically warns the operator of Low System Voltage. The default settings that are programmed at the factory are listed below.

#Voltage Monitoring
(Parameter – Default Setting)
Warning Setpoint – 20 VDC
Warning Delay – 10 Seconds
Hysteresis – 2 VDC
Security level – None (No password required)
  • If the voltage is below 20 VDC for 10 seconds, a warning will occur. To deactivate the warning, the voltage must rise above 22 VDC.
  • The setpoint can be programmed to a value between 20 and 22 VDC.
  • Open CAT ET and connect to the ECM. Read More: How to Connecting Caterpillar ET Software to the ECM.
  • Select Service - Monitoring System menu, then Low System Voltage.
Figure 1.2 - Service (Monitoring System)
Figure 1.3 - Low System Voltage (Monitoring System)

#Additional Note:
Derate - A reduction of engine horsepower in response to an abnormal operating condition.
Setpoint - A specific value which can activate the following responses: warning, deration and shutdown. The setpoint can be a pressure, a speed, a temperature, or a voltage.
Hysteresis - The change in the signal from a sensor that is tolerated by the ECM. The difference between the setpoint that activates a response and the value that deactivates the response. For example, a warning for low voltage can activate if a value below 20 VDC is detected by the ECM. The voltage must rise to 22 VDC in order to clear the warning. The hysteresis is the 2 VDC that are above the 20 VDC.

#Electrical Power Supply
Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine's Electronic Control Module (ECM) or if any one of the diagnostic/event codes below is active or easily repeated.
  • E043(1) Low System Voltage Warning - The battery voltage to the ECM is less than normal.
  • 168-0 Electrical System Voltage High - The battery supply voltage is greater than 32 VDC for two seconds. The engine's ECM has been powered for three seconds. The engine is not being cranked.
  • 168-1 Electrical System Voltage Low - The battery supply voltage is less than 9 VDC for two seconds. The engine's ECM has been powered for three seconds. The engine is not being cranked.
  • 168-2 Electrical System Voltage Erratic, Intermittent, or Incorrect - The engine is running. The battery voltage falls below 9 VDC for at least 6 seconds. The voltage returns above 9 VDC, or three voltage readings in the last 7 seconds were below 9 VDC.
Figure 1.4 - Electrical System Voltage (High/ 168-0)

To reduce resistance in the wiring harness, there are two isolated power connections to the ECM. The connections must be complete in order to ensure proper engine operation. There is a constant power supply to the ECM when the engine is shutdown. In order to shut off the power to the ECM, the main power needs to be disconnected.

The engine will begin the start-up when the following conditions exist:
• The ECM detects battery voltage at the keyswitch on P1-70.
• The Start/Run/Stop Switch is activated. Read More: Start/Run/Stop Switch on Caterpillar ET Software.
Figure 1.5 - Typical Schematic (3512C)

Test Step 1. Inspect Electrical Connectors and Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors.
C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
D. Check the ECM connector (allen head screw) for the proper torque.
E. Check the harness and the wiring for abrasion and for pinch points.
Expected Result: All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Test Step 2. Check the Battery Voltage
A. Measure no-load voltage at the battery posts.
B. Load test the batteries, using the Battery Load Tester.
Expected Result: The no-load voltage at the batteries is at least 23.5 VDC, and the batteries pass the load test.

Test Step 3. Check the Voltage at the ECM Connector
A. Disconnect the J1/P1 ECM connector.
B. Turn the main disconnect switch to the ON position.
C. Wiggle the harness during the following test steps in order to find an intermittent condition. Read More: Wiggle Test on Caterpillar ET Software.
-Measure the voltage between P1-52 (Unswitched Positive Battery) and P1-63 (Negative Battery).
-Measure the voltage between P1-53 (Unswitched Positive Battery) and P1-65 (Negative Battery).
-Measure the voltage between P1-70 (Keyswitch) and P1-63 (Negative Battery).
D. Turn the main disconnect switch to the OFF position.
E. Replace all wires and connectors to the original configuration.
Expected Result: The voltage is ± 1 VDC from the voltage at the battery terminals.

Test Step 4. Check the Voltage at the Customer Connector
A. Disconnect the customer connector.
B. Turn the main disconnect switch to the ON position.
C. Wiggle the harness during the following test steps in order to find an intermittent condition.
-Measure the voltage between Terminal 01 (Unswitched Positive Battery) and Terminal 34 (Negative Battery).
-Measure the voltage between Terminal 02 (Unswitched Positive Battery) and Terminal 35 (Negative Battery).
-Measure the voltage between Terminal 27 (Keyswitch) and Terminal 34 (Negative Battery).
D. Turn the main disconnect switch to the OFF position.
E. Replace all wires and connectors to the original configuration.
Expected Result: The voltage is ± 1 VDC from the voltage at the battery terminals.


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