G3520B Industrial Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the coolant temperature sensor or if any one of the diagnostic codes in Table 1 is active or easily repeated.

System Operation

Use this procedure to troubleshoot any suspect problems with the engine's coolant temperature sensor.

The sensor signal for the passive sensor is routed from the ECM to terminal 1 of the sensor connector. The sensor return for the passive sensors is routed from the ECM to terminal 2 of the sensor connector.

Illustration 1	g01420789
Schematic for the passive analog sensor

Illustration 2	g01420866
Location of the passive analog sensor (right front side engine view) (1) Engine coolant temperature sensor

Illustration 3	g01435647
Locations of the connectors at the terminal box for the master ECM (left front engine view) (2) J1/P1 ECM connectors (3) J7/P7 control harness connectors for the passive sensors

Illustration 4	g01420865
Terminal locations at the P1 ECM connector for the passive analog sensors (P1-3) Analog return (P1-27) Engine coolant temperature

Illustration 5	g01420881
Terminal locations at the P7 control harness connector for the passive analog sensor (P7-C) Engine coolant temperature (P7-P) Analog return (P7-Z) Shield

Illustration 6	g01436505
Terminal locations at the connector for the passive analog sensor (Terminal 1) Sensor signal (Terminal 2) Analog sensor return

Test Step 1. Check for Diagnostic Codes that are Active or Logged

1. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

2. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

3. Restore electrical power to the engine. Turn the engine control to the STOP position.

4. Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

5. Determine if a diagnostic code has occurred several times.

   Note: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a poor connection between a socket and a pin in a connector or of a poor connection between a wire and a terminal.

6. Determine if the problem is active and related to one of the following failure modes for the analog passive sensor:
   • -3

   • -4

7. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

Expected Result:

A diagnostic code is not active.

Results:

• OK - A diagnostic code is not active.

  Repair: There may be an intermittent electrical problem in the harness or in a connector. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting these problems.

  STOP

• Active -3 - An active -3 diagnostic code is present. The ECM detects an open in the circuit for the sensor. Proceed to Test Step 2.

• Active -4 - An active -4 diagnostic code is present. Proceed to Test Step 4.

Test Step 2. Check for Battery Voltage on the Signal Wire

1. Restore electrical power to the engine. Turn the engine control to the STOP position.

2. Measure the voltage on the harness side of the sensor connector between pin 1 and engine ground for the coolant temperature sensor.

3. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

Expected Result:

The signal voltage is less than battery voltage.

Results:

• OK - The signal voltage is less than battery voltage. The circuit for the signal is not shorted to the +Battery. Proceed to Test Step 3.

• Not OK - The signal voltage is equal to battery voltage.

  Repair: There is a short circuit to the +Battery in the harness. Repair the wiring harness or replace the wiring harness. Verify that the repair has resolved the original problem.

  STOP

Test Step 3. Create a Short Circuit at the Connector for the Coolant Temperature Sensor

1. Disconnect the harness connector for the coolant temperature sensor.

2. Fabricate a jumper wire that is long enough to create a test circuit across the harness side of the sensor connector. Crimp connector pins to each end of the jumper wire.

3. Install the jumper wire between terminal 1 (sensor signal) and terminal 2 (sensor return) at the sensor connector.

4. Restore electrical power to the engine. Turn the engine control to the STOP position.

5. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active -4 diagnostic code for the coolant temperature sensor.

   Wait at least 30 seconds in order for the diagnostic codes to become active.

6. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

Expected Result:

A -4 diagnostic code is now active for the coolant temperature sensor.

Results:

• OK - A -4 diagnostic code became active with the jumper wire in place.

  Repair: A -3 diagnostic code was active before creating the short at the sensor connector. A -4 diagnostic code became active after creating the short at the sensor connector. The wiring between the ECM and the sensor connector is OK. Perform the following procedure:Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - A -3 diagnostic code is still active for the coolant temperature sensor. There is an open circuit between the sensor connector and the ECM. There may be a problem with the ECM. Leave the sensor disconnected. Proceed to Test Step 5.

Test Step 4. Create an Open Circuit at the Connector for the Coolant Temperature Sensor

1. Disconnect the sensor connector for the coolant temperature sensor.

2. Restore electrical power to the engine. Turn the engine control to the STOP position.

3. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active -3 diagnostic code.

   Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

Expected Result:

A -3 diagnostic code is now active for the coolant temperature sensor.

Results:

• OK - A -3 diagnostic code becomes active while the sensor connector is disconnected.

  Repair: A -4 diagnostic code was active before disconnecting the sensor. A -3 diagnostic code became active after disconnecting the sensor. The wiring between the ECM and the sensor connector is OK. Perform the following procedure:Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - A -4 diagnostic code is still active for the coolant temperature sensor. There is a short circuit between the sensor connector and the ECM. There may be a problem with the ECM. Proceed to Test Step 5.

Test Step 5. Check for Proper Operation of the ECM

1. Fabricate a jumper wire that is long enough to create a test circuit between the ECM connector and the negative battery connection. Crimp a connector socket to one end of the jumper wire.

2. Disconnect the J1/P1 ECM connectors.

3. Use a wire removal tool to remove the wire from terminal location J1-27 at the ECM connector.

4. Install the socket end of the jumper wire into this terminal location.

5. Connect the J1/P1 ECM connectors.

6. Check the operation of the ECM by creating an open circuit at the ECM.

   1. During this portion of the test, be sure to hold the loose end of the jumper wire away from any ground source in order to create an open circuit condition.

   2. Restore electrical power to the engine. Turn the engine control to the STOP position.

   3. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      An open circuit diagnostic code -3 should be active for the coolant temperature sensor.

7. Check the operation of the ECM by creating a short at the ECM.

   1. Install the loose end of the jumper wire that is for the signal wire to the ECM ground strap. Ensure that a good connection is made to the engine ground.

   2. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait for at least 30 seconds for activation of the code.

      A -4 diagnostic code should be active when the wire jumper is connected to engine ground.

   3. Turn the engine control to the OFF/RESET position. Remove electrical power from the engine.

   4. Remove the jumper wire. Restore the wiring to the original configuration.

Expected Result:

A -3 diagnostic code is active while the jumper wire is not grounded to engine ground. A -4 diagnostic code is active while the jumper wire is connected to the engine ground.

Results:

• OK - The correct diagnostic codes became active during the test procedure.

  Repair: The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the sensor.The problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor. Verify that the original condition has been resolved.

  STOP

• Not OK - One of the following conditions exists: The -3 diagnostic code is not active when the open circuit condition is present on the signal wire of the coolant temperature sensor. The -4 diagnostic code is not active when the signal wire for the coolant temperature sensor is connected to engine ground.

  Repair: The ECM is not operating properly. Perform the following procedure:Temporarily install a new master ECM. Refer to Troubleshooting, "ECM - Replace".If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP