3500B and 3500C Locomotive Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensors 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 following sensors:

• Atmospheric pressure sensor

• Aftercooler temperature sensor

• Coolant temperature sensor

• Crankcase pressure sensor

• Filtered engine oil pressure sensor

• Filtered fuel pressure sensor

• Turbocharger outlet pressure sensor

• Left turbocharger inlet pressure sensor

• Right turbocharger inlet pressure sensor

• Unfiltered engine oil pressure sensor

• Unfiltered fuel pressure sensor

The supply voltage is routed to terminal A of each sensor connector. The sensor return is routed to terminal B of each sensor connector. The sensor signal is routed to terminal C of each sensor connector. The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

The ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine is off for at least five seconds. During an automatic calibration, the ECM calibrates pressure sensors to the value of the atmospheric pressure sensor and against an acceptable offset pressure range.

The ECM continuously outputs a pull-up voltage on the input terminal from an analog sensor. The ECM uses this pull-up voltage in order to detect an open or a short in the signal circuit. When the ECM detects the presence of a voltage that is above the normal range of the sensor on the signal circuit, the ECM will generate an open circuit diagnostic code -3 for that sensor. When the ECM detects the absence of the pull-up voltage on the signal circuit, the ECM will generate a short circuit diagnostic code -4 for that sensor. The presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are not open or shorted to ground.

Illustration 1	g01257792
Typical schematic

Illustration 2	g01257833
Front and rear view (typical example) (1) Unfiltered engine oil pressure sensor (2) Turbocharger compressor outlet pressure sensor (3) Atmospheric pressure sensor (4) Left turbocharger compressor inlet pressure sensor (5) Right turbocharger compressor inlet pressure sensor

Illustration 3	g01257823
Left side view (typical example) (6) Unfiltered fuel pressure sensor (7) Filtered fuel pressure sensor (8) Filtered engine oil pressure sensor (9) Coolant temperature sensor (10) Atmospheric pressure sensor (11) Aftercooler temperature sensor

Illustration 4	g01257828
Right side view (typical example) (12) Crankcase pressure sensor

Illustration 5	g01257798
P1 ECM connector (P1-2) 5 V sensor supply (P1-3) Sensor return (P1-6) Aftercooler temperature sensor (P1-7) Coolant temperature sensor (P1-16) Filtered engine oil pressure sensor (P1-17) Unfiltered engine oil pressure sensor (P1-24) Filtered fuel pressure (P1-25) Unfiltered fuel pressure

Illustration 6	g01212480
P2 ECM connector (P2-36) Turbocharger outlet pressure sensor (P2-37) Atmospheric sensor (P2-38) Left turbocharger inlet pressure sensor (P2-39) Right turbocharger inlet pressure sensor (P2-46) Crankcase pressure sensor

Illustration 7	g01234146
Location of ECM connectors

Illustration 8	g01094844
Sensor connector (Pin A) Sensor supply (Pin B) Sensor return (Pin C) Signal

Test Step 1. CHECK FOR "ACTIVE" OR "LOGGED" DIAGNOSTIC CODES

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

2. Restore electrical power to the ECM.

3. 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.

4. 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 bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal. The problem may be caused by moisture, corrosion, or wear.

5. Determine if the problem is active and related to one of the following diagnostic codes:

   • -3

   • -4

Expected Result:

A diagnostic code is not active.

Results:

• OK - A diagnostic code is not active.

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

  STOP

• Not OK - A diagnostic code is active. Proceed to Test Step 2.

Test Step 2. CHECK THE 5 VOLT SUPPLY VOLTAGE AT THE SENSOR CONNECTOR

1. Do not disconnect the suspect connector.

2. Connect a voltmeter between pin A and pin B on the sensor side of the connector for the suspect sensor(s).

3. Measure the voltage between pin A and pin B for the suspect sensor(s).

4. Wiggle the harness while you monitor the voltage on the voltmeter. Perform the 45 N (10 lb) pull test on each wire in the circuit. Each terminal and each connector should easily withstand 45 N (10 lb) of tension and each wire should remain in the connector body. This test checks whether the wire was properly crimped in the terminal and whether the terminal was properly inserted into the connector.

Expected Result:

The supply voltage is 5.0 ± 0.5 VDC.

Results:

• OK - The voltage is 5.0 ± 0.5 VDC. An active -3 diagnostic code is present. Proceed to Test Step 3.

• OK - The voltage is 5.0 ± 0.5 VDC. An active -4 diagnostic code is present. Proceed to Test Step 5.

• Not OK - The voltage is not 5.0 ± 0.5 VDC. Proceed to Test Step 7.

Test Step 3. CHECK FOR A SHORT TO THE +BATTERY AT THE SENSOR CONNECTOR

1. Measure the voltage on the harness side of the sensor connector between pin B and pin C for the suspect sensor(s).

Expected Result:

The supply voltage is less than battery voltage.

Results:

• OK - The supply voltage is less than battery voltage. Proceed to Test Step 4.

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

  Repair: There is a short in the harness to the +Battery. Repair the wiring.

  STOP

Test Step 4. CREATE A SHORT AT THE SENSOR CONNECTOR

1. Remove electrical power from the ECM.

2. Disconnect the suspect sensor(s).

3. Use a wire jumper in order to create a short between terminal C (signal) and terminal B (sensor return) at the connector for the suspect sensor(s).

4. Restore electrical power to the ECM.

5. Monitor the diagnostic codes on Cat ET. Check for an active -4 diagnostic code for the suspect sensor(s).

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

6. Remove electrical power from the ECM.

Expected Result:

A -4 diagnostic code is now active for the suspect sensor(s).

Results:

• OK - 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 harness and the ECM are OK. There may be a problem with the sensor.

  Repair: 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 suspect sensor(s). The problem may be in the harness or with the ECM. Proceed to Test Step 6.

Test Step 5. CREATE AN OPEN AT THE SUSPECT SENSOR CONNECTOR

1. Remove electrical power from the ECM.

2. Disconnect the sensor connector of the suspect sensor(s) with the active -4 diagnostic code.

3. Restore electrical power to the ECM.

4. Monitor the diagnostic codes on Cat ET. Check for an active -3 diagnostic code for the suspect sensor(s).

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

5. Remove electrical power from the ECM.

Expected Result:

A -3 diagnostic code is now active for the suspect sensor(s).

Results:

• OK - A -4 diagnostic code was active before disconnecting the sensor. A -3 diagnostic code became active after disconnecting the sensor. The harness and the ECM are OK. There may be a problem with the sensor.

  Repair: 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 suspect sensor(s). Leave the sensor disconnected. The problem may be in the harness or with the ECM. Proceed to Test Step 6.

Test Step 6. TEST THE OPERATION OF THE ECM

1. Fabricate a jumper wire that can be used to replace the signal wire in the ECM connector for the suspect sensor(s). Crimp a connector socket to one end of the jumper wire.

2. Disconnect the appropriate ECM connector for the suspect sensor(s).

3. Remove the signal wire for the suspect sensor(s) from the ECM connector.

4. Install the jumper wire into the terminal location for the suspect sensor(s) at the ECM connector.

5. Connect the ECM connector.

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

   1. Hold the loose end of the jumper wire away from any components in order to create an open circuit condition.

   2. Restore electrical power to the ECM.

   3. Monitor the active diagnostic code screen on Cat ET. Check for a -3 diagnostic code for the suspect sensor(s).

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

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

   1. Short the jumper wire for the suspect sensor(s) to engine ground in order to create a short circuit condition.

   2. Monitor the active diagnostic code screen on Cat ET. Check for a -4 diagnostic code for the suspect sensor(s).

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

8. Remove electrical power from the ECM.

9. Remove all jumper wires. Return the wiring to the original configuration.

Expected Result:

A -3 diagnostic code is active when the sensor signal wire is removed from the ECM connector. A -4 diagnostic code is active when the signal wire is connected to engine ground.

Results:

• OK - The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the sensor.

  Repair: If the code is active for more than one sensor, the problem is most likely in the return wire for the sensor. Repair the return wire for the sensor or replace the harness.

  If the code is only active for one sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor.

  STOP

• Not OK - One of the following conditions exists: The -3 diagnostic code is not active when the sensor signal wire is disconnected. The -4 diagnostic code is not active when the wire jumper is shorted to ground.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP

Test Step 7. CHECK THE SUPPLY VOLTAGE AT THE ECM

1. Remove electrical power from the ECM.

2. Remove the supply wire from the appropriate ECM connector. Install a wire jumper(s) into the socket(s) for the sensor supply.

3. Restore electrical power to the ECM.

4. Measure the voltage between the wire jumper(s) and engine ground.

5. Remove electrical power from the ECM.

6. Remove the wire jumpers and replace all wires.

Expected Result:

The supply voltage is 5.0 ± 0.5 VDC.

Results:

• OK - The supply voltage is 5.0 ± 0.5 VDC. The supply voltage at the ECM is correct. There is a problem in the wiring between the ECM and the sensor connector. Check the supply wire and the return wire for an open circuit.

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

  STOP

• Not OK - The supply voltage is not 5.0 ± 0.5 VDC. The voltage at the ECM is not correct.

  Repair: Verify that battery voltage is present at the ECM on the battery connections and on the keyswitch input. If the correct voltage is present, replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP