3512B and 3512C Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensors. Also, use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.

Table 1

Diagnostic Codes Table
Description	Conditions which Generate this Code	System Response
94-3 Engine Fuel Delivery Pressure : Voltage Above Normal	The Electronic Control Module (ECM) detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
94-4 Engine Fuel Delivery Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
100-3 Engine Oil Pressure : Voltage Above Normal	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
100-4 Engine Oil Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
101-3 Engine Crankcase Pressure : Voltage Above Normal	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
101-4 Engine Crankcase Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for at least 3 seconds.
273-3 Turbo Outlet Pressure : Voltage Above Normal	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
273-4 Turbo Outlet Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
274-3 Atmospheric Pressure : Voltage Above Normal	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
274-4 Atmospheric Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
275-3 Right Turbo Inlet Pressure : Voltage Above Normal	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
275-4 Right Turbo Inlet Pressure : Voltage Below Normal	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
276-3 Left Turbo Inlet Pressure open/short to +batt	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
276-4 Left Turbo Inlet Pressure short to ground	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
279-3 Aftercooler Temperature open/short to +batt	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
279-4 Aftercooler Temperature short to ground	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.
542-3 Unfiltered Engine Oil Pressure open/short to +batt	The ECM detects signal voltage that is above normal for one second. The ECM has been powered for at least 3 seconds.	The code is logged.
542-4 Unfiltered Engine Oil Pressure short to ground	The ECM detects signal voltage that is below normal for one second. The ECM has been powered for 3 seconds.

System Operation

Use this procedure to troubleshoot any suspect problems with the following sensors for the primary and/or secondary ECM:

• Aftercooler temperature sensor

• Atmospheric pressure 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

Background Information

The ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine is off for at least 5 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 creates a pull-up voltage on the signal wire for each sensor. The ECM uses this pull-up voltage in order to detect a problem in the signal circuit. When the ECM detects voltage that is above a threshold on the signal wire, the ECM activates a high voltage -3 diagnostic code. When the ECM detects voltage that is below a threshold on the signal wire, the ECM activates a low voltage -4 diagnostic code.

Note: There may be a delay of 30 seconds in order for Caterpillar Electronic Technician (ET) to display an active diagnostic code. When you check for a diagnostic code, be sure to wait at least 30 seconds.

The following components can cause these codes:

• Electrical connector or wiring

• Sensor

• ECM

The most likely cause of a code is a problem with an electrical connector or wiring. The least likely cause of a code is the ECM.

Illustration 1	g03317117
Analog active sensor schematic

Illustration 2	g03321053
Terminal locations at the P1 ECM connectors for the analog sensors (P1-2) Analog supply (P1-3) Analog return (P1-16) Filtered oil pressure (P1-17) Unfiltered oil pressure (P1-24) Filtered fuel pressure (P1-25) Unfiltered fuel pressure (P1-35) Analog return (P1-39) Analog supply

Illustration 3	g03321404
Terminal locations at the P2 ECM connector for the analog sensors (P2-36) Turbo outlet pressure (P2-37) Atmospheric pressure (P2-38) Left turbo inlet pressure (P2-39) Right turbo inlet pressure (P2-46) Crankcase pressure

Illustration 4	g01240891
Sensor connector (Terminal 1) Sensor supply (Terminal 2) Sensor return (Terminal 3) Signal

Table 2

Troubleshooting Test Steps	Values	Results
1. Determine if the Code is Logged or Active A. Connect Cat ET to the service tool connector. B. Restore electrical power to the engine ECM. C. Monitor the active diagnostic code and the logged diagnostic codes on Cat ET. Note. Wait at least 30 seconds in order for diagnostic codes to become active. D. Identify the diagnostic code.	Active or logged code	Results: Logged code Repair: Do not troubleshoot a logged code unless the code relates to an operator complaint. If the code is logged and the code does not relate to an operator complaint, clear the code. If the code is logged, and the code relates to an operator complaint. Proceed to Test Step 2 Results: Active code Proceed to Test Step 3
2. Check the Integrity of the Connections at the Connectors A. Restore the electrical power to the ECM. Do not start the engine. B. Install a 7X-1708 Multimeter Probe (RED) and a 7X-1709 Multimeter Probe (BLACK) onto the test leads of a multimeter. Note: Ensure that the multimeter probes are in good repair. Bent probes may contact other terminals inside the connector. C. Check for an intermittent problem at the connector for the suspect sensor: Note: Do not disconnect any harness connectors in order to perform this procedure. a. Carefully insert the probes into the terminal locations for the sensor supply and the sensor return at the appropriate ECM connector. b. While you observe the voltage reading on the multimeter, wiggle the wires and pull on the wires at the connector for the suspect sensor. The voltage reading will not vary more than 0.5 V for a solid electrical connection. c. Remove the probes from the connector. D. Check for an intermittent problem at the ECM connector: Note: Do not disconnect any harness connectors in order to perform this procedure. a. Carefully insert the probes into the terminal locations for the sensor supply and the sensor return at the connector for the suspect sensor. b. Observe the voltage reading on the multimeter. Wiggle the harness and pull on the wires for the sensor supply and the sensor return at the ECM connector. The voltage reading will not vary more than 0.5 V for a solid electrical connection. c. Remove the probes from the connector.	0.5V Tolerance	Results: The voltage reading did not vary more than 0.5 V. Repair: The connections are OK at the connectors. There does not appear to be an intermittent problem in the circuit at this time. Return the engine to service. Results: At least one of the voltage reading varied more than 0.5 V during the test. Repair: Disconnect the suspect connector and inspect the connector and the terminals for moisture, damage, and corrosion. Repair the connectors and/or the terminals. Verify that the repair eliminated the problem.
3. Check the Supply Voltage at the Sensor Connector A. Measure the voltage between terminal 1 (sensor supply) and terminal 2 (sensor return) at the harness connector for the sensor that relates to the code.	4.5 to 5.5 VDC	Results: The voltage is between 4.5 VDC and 5.5 VDC. The supply voltage is at the sensor connector. Record the voltage measurement. If you are troubleshooting a -3 diagnostic code. Proceed to Test Step 4 If you are troubleshooting a -4 diagnostic code. Proceed to Test Step 7 Results: The voltage is less than 4.5 VDC or the voltage is greater than 5.5 VDC. Repair: The voltage of the sensor supply is incorrect. Refer to Troubleshooting, "Sensor Supply - Test"
4. Check for Battery Voltage on the Signal Wire A. Measure the voltage between the signal terminal and the return terminal on the harness connector for the sensor that relates to the diagnostic code. B. Turn the main disconnect switch to the OFF position.	Battery voltage	Results: The voltage measurement is less than the +Battery voltage. The signal wire is not shorted to the +Battery. Proceed to Test Step 5 Results: The voltage measurement is approximately the +Battery voltage. The signal wire is shorted to the +Battery. Repair: Repair the wiring, when possible. Replace parts, if necessary. Verify that the repair eliminated the problem.
5. Check the Signal Wire for an Open Circuit A. Disconnect the sensor that relates to the diagnostic code. B. Connect a jumper wire between the signal terminal and the return terminal on the harness connector for the sensor that relates to the diagnostic code. This jumper will replace the sensor with a short circuit. C. Restore the electrical power to the ECM. D. Look for a -4 diagnostic code.	Open circuit	Results: The -3 code does not change to a -4 code when the jumper wire is connected. Connect the sensor. There is a problem with the wiring harness or with the ECM. Proceed to Test Step 6 Results: The -3 code changes to a -4 code when the jumper wire is connected. The wiring harness and the ECM are OK. Repair: Perform the following procedure: 1. Remove the jumper wire. 2. Connect a new sensor to the engine harness. Do not install the sensor into the engine. 3. Verify that the active -3 diagnostic code does not recur. 4. Install the sensor into the engine. 5. Clear all logged diagnostic codes. Verify that the repair eliminated the problem.
6. Check the ECM for Proper Operation A. Turn the main disconnect switch to the OFF position. B. Determine the terminal location at the appropriate ECM connector for the signal and return wires of the suspect sensor. C. Remove the signal terminal and the return terminal from the ECM connector. D. Install a jumper wire between the terminal locations for the signal and the return at the ECM connector. This jumper will replace the engine wiring with a short circuit. E. Restore the electrical power to the ECM. F. Look for a -4 diagnostic code.	ECM	Results: A -4 code is active when the jumper wire is installed. The ECM detected the jumper wire at the ECM connector. However, the ECM did not detect the jumper wire at the harness connector for the sensor. There is an open circuit in the wiring. Repair: Repair the wiring, when possible. Replace parts, if necessary. Verify that the repair eliminated the problem. Results: A -4 code is not active when the jumper wire is installed. Repair: The ECM does not detect the jumper wire at the ECM connector. There appears to be a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Test ECM Mode". Note: Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) for assistance.
7. Check the Signal Wire for a Short Circuit A. Disconnect the sensor that applies to the -4 diagnostic code. B. Look for a -3 diagnostic code. C. Connect the sensor and look for a -4 diagnostic code.	Short circuit	Results: When the sensor is disconnected, the -4 code remains. There is a problem with the wiring harness or with the ECM. Proceed to Test Step 8 Results: When the sensor is disconnected, the -4 code changes to a -3 code. Repair: Perform the following procedure: 1. Connect a new sensor to the engine harness. Do not install the sensor into the engine. 2. Verify that the active -4 diagnostic code does not recur. 3. Install the sensor into the engine. 4. Clear all logged diagnostic codes. Verify that the repair eliminated the problem.
8. Check the ECM for Proper Operation A. Determine the terminal location at the appropriate ECM connector for the signal wire of the suspect sensor. B. Remove the signal wire from the ECM connector. C. Check if the -4 diagnostic code becomes an active -3 active code.	ECM	Results: A -3 code is active when the signal wire is disconnected from the connector at the ECM. The ECM detected the open circuit at the ECM connector. However, the ECM did not detect the open circuit at the harness connector for the sensor. There is a problem with the wiring between the ECM connector and the harness connector for the sensor. There may be a problem with a connector. Repair: Repair the wiring or the connector, when possible. Replace parts, if necessary. Verify that the repair eliminated the problem. Results: A -3 code is not active when the signal wire is disconnected from the ECM connector. The ECM did not detect the open circuit at the ECM connector. There is a problem with the ECM. Repair: The ECM does not detect the open circuit at the ECM connector. There appears to be a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Test ECM Mode". Note: Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) for assistance.

If the procedure did not correct the issue, contact your Cat Dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).