3176C, 3406E and 3456 Industrial Engines Troubleshooting – Electrical Power Supply – Test

System Operation Description:

Use this test if there are intermittent engine shutdowns or if a difficulty in starting is not accompanied by loss of electrical accessories. Engine shutdowns that are accompanied by a loss of other electrical accessories indicate a problem in the keyswitch. This does not indicate a problem in the wiring at the engine’s Electronic Control Module (ECM). Verify that there are no problems with the starting system or the charging system before you use this test.

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine’s ECM or if any one of the diagnostic codes in Table 1 is active or easily repeated.

Table 1

Diagnostic Codes Table
Code and Description	Conditions which Generate this Code	System Response
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.	The code is logged.
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 momentarily drops below 9 VDC or the voltage drops below 9 VDC for three voltage readings in the last seven seconds.

Unswitched battery voltage is supplied to the ECM at terminal P1-4. The negative battery is supplied to the ECM at terminal P1-5. The ECM receives the input from the keyswitch at terminal P1-6 when the keyswitch is in the ON position or in the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down. The ECM continuously receives battery voltage through the circuit breaker for the engine ECM.

The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).

Illustration 1 g01428248
Schematic for the electrical power supply

Test Step 1. Inspect the Electrical Connectors and the Wiring

 

1. Remove electrical power from the ECM.

Illustration 2 g01139425
ECM
(1) J1/P1 connectors
(2) J2/P2 connectors

2. Thoroughly inspect ECM connector J1/P1, ECM connector J2/P2, and all other connectors in the wiring harness. Refer to Troubleshooting, “Electrical Connectors – Inspect”.

Illustration 3 g01450608
P1 terminals that are associated with the electrical power supply circuit

(P1-4) Unswitched +Battery

(P1-5) −Battery

(P1-6) Switched +Battery

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector.

 

4. Check the allen head screw on each of the ECM connectors for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque values.

 

5. Check the harness and wiring for abrasions and for pinch points from the batteries to the ECM.

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.

Results:

 

• OK – The harness and wiring appear to be OK. Proceed to Test Step 2. 
• Not OK – There is a problem in the connectors and/or wiring.Repair: Repair the circuit. Ensure that all of the seals are properly in place and that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Battery Voltage at the ECM

 

1. Disconnect the J1/P1 ECM connector.

 

2. Restore electrical power to the ECM.

 

3. Turn the keyswitch to the ON position.

 

4. Measure the voltage between terminal P1-4 (unswitched +Battery) and terminal P1-5 (−Battery).

 

5. Measure the voltage between terminal P1-6 (switched +Battery) and terminal P1-5 (−Battery).

Expected Result:

The supply voltage is at least 11 VDC for a 12 volt system. The supply voltage is at least 22 VDC for a 24 volt system.

Results:

 

• OK – The ECM is receiving the correct voltage.Repair: If an intermittent condition is suspected, refer to Troubleshooting, “Electrical Connectors – Inspect”.

  STOP

   

• Not OK – Unswitched power out of range – The voltage is not correct at the ECM. Proceed to Test Step 3. 
• Not OK – Switched voltage out of range – Proceed to Test Step 4.

Test Step 3. Check the Batteries

 

1. Measure the no-load battery voltage at the battery posts.

 

2. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, “Use of 4C-4911 Battery Load Tester for 6, 8 and 12 Volt Lead Acid Batteries” and Special Instruction, SEHS7633, “Battery Test Procedure”.

Expected Result:

The batteries pass the load test. The measured voltage satisfies the minimum specification.

Results:

 

• OK – The batteries are OK.Repair: There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the 15 Amp circuit breaker for the ECM is not tripped. Verify that the connection at the engine ground stud is clean and tight and that the battery disconnect switch is functioning properly. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

   

• Not OK – The battery voltage is low or the battery did not pass the load test.Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Check the Voltage from the Keyswitch to the ECM

 

1. Remove electrical power from the ECM.

 

2. Turn the keyswitch to the OFF position.

 

3. Remove the wire from the terminal R of the keyswitch.

 

4. Restore electrical power to the engine ECM.

 

5. Turn the keyswitch to the ON position.

 

6. Measure the voltage on terminal B of the keyswitch to engine ground.

 

7. Measure the voltage on terminal R of the keyswitch to engine ground.

 

8. Turn the keyswitch to the OFF position.

Expected Result:

Voltage is present on terminal B and terminal R at the keyswitch.

Results:

 

• OK – Voltage is present on terminal B and terminal R at the keyswitch.Repair: If voltage is present on terminal R, repair the circuit between the keyswitch and the ECM. Ensure that the main power relay for the machine is receiving the correct control. Check the condition of the fuse that is in the circuit for the keyswitch. Verify that the problem is eliminated.

  STOP

   

• Not OK – Voltage is not present on terminal B at the keyswitch.Repair: If voltage is not present on terminal B, repair the wire between the +Battery and the keyswitch. Verify that the circuit breaker for the keyswitch is not tripped. Verify that the problem is eliminated.

  STOP

   

• Not OK – Voltage is not present on terminal R at the keyswitch.Repair: If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is eliminated.

  STOP