3512C and 3516C Engines Caterpillar

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 codes in Table 1 is active or easily repeated.

The engine's ECM receives 24 VDC from the battery. Electrical power comes from the 20 amp breaker for the ECM to the normally close contacts of relay "R2A". The electrical power to the ECM from the normally closed contact of relay "R2A" is on wire C150 and on wire 150. The wire C150 goes to pin P1-53 of ECM connector J1/P1. The wire 150 goes to pin P1- 52 of ECM connector J1/P1. The −Battery is applied to pin P1-63 and pin P1-65 of ECM connector J1/P1. The wire numbers for the −Battery are wire D229 and wire 229 .

The Engine Control Switch (ECS) sends a signal to pin P1-70 of the ECM when the ECS is in the following positions: REMOTE, STOP and START. When the ECM senses battery voltage on pin P1-70 of the ECM, the ECM will power up. When the ECS is in the OFF/RESET position, voltage is not present on P1-70 and the ECM will power down.

When the emergency stop switch is activated, relays"R4" and "R4A" energize. Electrical power from relay "R4A" is routed to terminal 3 of the timer. When 24 VDC is applied to terminal 3 of the timer, the timer activates for 2.5 seconds. The timer outputs 24 VDC to the coil of the air shutoff switch (ASOS). The timer also outputs 24 VDC to the diode assembly and to the coils of relay "R3A" and relay "R3". When relay "R3A" is energized, power is applied to the coil of relay "R2A". When relay "R2A" is energized, the normally closed contacts of relay "R2A" open. This removes electrical power to the ECM.

In order to restart the engine, the operator must correct the cause of the emergency stop condition. The ECS must be turned to the OFF/RESET position for three seconds. This resets the ECM and the air shutoff timer. In addition to turning the ECS to the OFF/RESET position, the operator must manually open the air shutoff valves before starting the engine.

The presence of two +Battery connections and two −Battery connections to the ECM reduce harness resistance. All of these connections must be complete in order to ensure proper engine operation.

Illustration 1	g01199226
Typical example

Illustration 2	g01218324
P1 ECM connector (P1-52) +Battery (P1-53) +Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch

Illustration 3	g01234146
Location of ECM connectors

Note: If a remote START switch is installed, the remote START switch must be in the STOP position for this test.

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the ECS to the OFF/RESET position.

2. Turn the circuit breaker for the battery to the OFF position.

3. Verify that the circuit breakers are not tripped.

4. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

5. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

6. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct torque values.

7. 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, and the harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The connectors and wiring are OK. Proceed to Test Step 2.

• Not OK - The connectors and/or wiring need repair.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 2. Check the Voltage to the ECM

1. Disconnect the ECM connector J1/P1.

2. Turn the circuit breaker for the battery to the ON position.

3. Turn the ECS to the STOP position.

   Note: Verify that wire D229 and wire 229 have continuity from the ECM to the −Battery terminal.

4. Measure the voltage at the ECM. Measure the voltage between P1-53 and P1-65. Measure the voltage between P1-52 and P1-63.

5. Measure the voltage between P1-70 and P1-65 at the ECM.

Expected Result:

The voltage is 24 ± 3 VDC. The difference between the three voltage measurements is less than 0.5 VDC.

Results:

• OK - The ECM is receiving the correct voltage.

  Repair: The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• OK - The voltage is more than 24 ± 3 VDC.

  Repair: There is a problem with the alternator. Refer to Specifications, "Alternator and Regulator" for information on the charging system.

  STOP

• Not OK - The voltage is less than 24 ± 3 VDC. The wiring or components between the battery and the ECM may be preventing the voltage from reaching the ECM. Proceed to Test Step 3.

• Not OK - P1-70 - The voltage is less than 24 ± 3 VDC on the input for the keyswitch to the ECM. Proceed to Test Step 6.

Test Step 3. Check the Battery Voltage

1. Turn the circuit breaker for the battery to the OFF position.

2. Turn the ECS to the OFF/RESET position.

3. Measure no-load battery voltage at the battery terminals. Refer to Testing and Adjusting, "Test Tools for the Electrical System" for the proper procedures to check the batteries.

4. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249. Refer to Special Instruction, SEHS7633.

Expected Result:

The no-load voltage at the batteries is at least 23.5 VDC and the batteries pass the load test.

Results:

• OK - The battery voltage is OK and the battery passes the load test. Proceed to Test Step 4.

• Not OK - The battery voltage is incorrect and/or the battery fails the load test.

  Repair: The batteries or the alternator are causing the problem. Recharge the batteries or replace the batteries. Verify that the original condition is resolved.

  STOP

Test Step 4. Check the Voltage at Relay " R2A"

1. Remove wire A150 from terminal 30 of relay "R2A".

2. Measure the voltage from wire A150 to the −Battery terminal.

3. Reconnect wire A150 to terminal 30 of relay "R2A".

Expected Result:

The voltage is 24 ± 3 VDC.

Results:

• OK - The voltage is 24 ± 3 VDC. Proceed to Test Step 5.

• Not OK - The voltage is not 24 ± 3 VDC.

  Repair: Verify that voltage is present at the breaker for the ECM. If voltage is present at the breaker for the ECM, repair the wire A150 between the breaker for the ECM and relay "R2A".

  If voltage is not present at the breaker for the ECM, check the wiring between the battery and the breaker for the ECM. Verify that the breaker for the ECM is not tripped and that the breaker for the ECM is operating correctly.

  STOP

Test Step 5. Check the Voltage at Terminal 87A of Relay "R2A"

1. Remove wire A150 and wire 150 from terminal 87A of relay "R2A".

2. Measure the voltage from terminal 87A of relay "R2A" to the −Battery terminal.

Expected Result:

The voltage is 24 ± 3 VDC.

Results:

• OK - The voltage is 24 ± 3 VDC.

  Repair: The wiring between relay "R2A" and the ECM connector P1 is damaged. Check wire C150 and wire 150 between relay "R2A" and the ECM connector P1.

  STOP

• Not OK - The voltage is not 24 ± 3 VDC.

  Repair: Verify that relay "R2A" is not energized. Relay "R2A" will be energized under the following conditions:

  • The local emergency stop is activated.

  • The remote emergency stop is activated.

  • A short to the +Battery is present on the wire T120 that goes to the coil of relay "R2A".
  If the coil of relay "R2A" is not energized, the contact of relay "R2A" is damaged. Replace relay "R2A".

  STOP

Test Step 6. Check the Voltage at the Engine Control Switch (ECS)

1. Remove wire 113 from terminal 16 of the ECS.

2. Turn the ECS to the STOP position.

3. Measure the voltage at the ECS when the switch is in the STOP position. Measure the voltage between terminal 16 and engine ground. Measure the voltage between terminal 19 and engine ground.

Expected Result:

The voltage is 24 ± 3 VDC on both terminals.

Results:

• OK - The voltage is 24 ± 3 VDC on both terminals.

  Repair: The wire 113 between terminal 16 of the ECS and pin P1-70 of the ECM needs repair. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

• Not OK - Terminal 16 - The correct voltage is not present on terminal 16 of the ECS.

  Repair: If 24 ± 3 VDC is present on terminal 19 of the ECS, replace the ECS.

  STOP

• Not OK - Terminal 19 - The correct voltage is not present on terminal 19 of the ECS.

  Repair: Repair the wire C150 between terminal 19 of the ECS and the R2A relay.

  STOP